Part I: Fundamentals of Software Testing
Part II – Software Testing for various Architectures
Part III – Platform Specific Testing
2. What is Software Testing and Why is it Important?
A brief history of Software engineering and the SDLC.
The software industry has evolved through 4 eras, 50’s –60’s, mid 60’s –late 70’s, mid 70’s- mid 80’s, and mid 80’s-present. Each era has its own distinctive characteristics, but over the years the software’s have increased in size and complexity. Several problems are common to almost all of the eras and are discussed below.
The Software Crisis dates back to the 1960’s when the primary reasons for this situation were less than acceptable software engineering practices. In the early stages of software there was a lot of interest in computers, a lot of code written but no established standards. Then in early 70’s a lot of computer programs started failing and people lost confidence and thus an industry crisis was declared. Various reasons leading to the crisis included:
Hardware advances outpacing the ability to build software for this hardware.
The ability to build in pace with the demands.
Increasing dependency on software’s
Struggle to build reliable and high quality software
Poor design and inadequate resources.
This crisis though identified in the early years, exists to date and we have examples of software failures around the world. Software is basically considered a failure if the project is terminated because of costs or overrun schedules, if the project has experienced overruns in excess of 50% of the original or if the software results in client lawsuits. Some examples of failures include failure of Air traffic control systems, failure of medical software, and failure in telecommunication software. The primary reason for these failures other than those mentioned above is due to bad software engineering practices adopted. Some of the worst software practices include:
No historical software-measurement data.
Rejection of accurate cost estimates.
Failure to use automated estimating and planning tools.
Excessive, irrational schedule pressure and creep in user requirements.
Failure to monitor progress and to perform risk management.
Failure to use design reviews and code inspections.
To avoid these failures and thus improve the record, what is needed is a better understanding of the process, better estimation techniques for cost time and quality measures. But the question is, what is a process? Process transform inputs to outputs i.e. a product. A software process is a set of activities, methods and practices involving transformation that people use to develop and maintain software.
At present a large number of problems exist due to a chaotic software process and the occasional success depends on individual efforts. Therefore to be able to deliver successful software projects, a focus on the process is essential since a focus on the product alone is likely to miss the scalability issues, and improvements in the existing system. This focus would help in the predictability of outcomes, project trends, and project characteristics.
The process that has been defined and adopted needs to be managed well and thus process management comes into play. Process management is concerned with the knowledge and management of the software process, its technical aspects and also ensures that the processes are being followed as expected and improvements are shown.
From this we conclude that a set of defined processes can possibly save us from software project failures. But it is nonetheless important to note that the process alone cannot help us avoid all the problems, because with varying circumstances the need varies and the process has to be adaptive to these varying needs. Importance needs to be given to the human aspect of software development since that alone can have a lot of impact on the results, and effective cost and time estimations may go totally waste if the human resources are not planned and managed effectively. Secondly, the reasons mentioned related to the software engineering principles may be resolved when the needs are correctly identified. Correct identification would then make it easier to identify the best practices that can be applied because one process that might be suitable for one organization may not be most suitable for another.
Therefore to make a successful product a combination of Process and Technicalities will be required under the umbrella of a well-defined process.
Having talked about the Software process overall, it is important to identify and relate the role software testing plays not only in producing quality software but also maneuvering the overall process.
The computer society defines testing as follows: “Testing -- A verification method that applies a controlled set of conditions and stimuli for the purpose of finding errors. This is the most desirable method of verifying the functional and performance requirements. Test results are documented proof that requirements were met and can be repeated. The resulting data can be reviewed by all concerned for confirmation of capabilities.”
There may be many definitions of software testing and many which appeal to us from time to time, but its best to start by defining testing and then move on depending on the requirements or needs.
3. Types of Development Systems
The type of development project refers to the environment/methodology in which the software will be developed. Different testing approaches need to be used for different types of projects, just as different development approaches.
3.1 Traditional Development Systems
The Traditional Development System has the following characteristics:
• The traditional development system uses a system development methodology.
• The user knows what the customer requires (Requirements are clear from the customer).
• The development system determines the structure of the application.
What do you do while testing:
• Testing happens at the end of each phase of development.
• Testing should concentrate if the requirements match the development.
• Functional testing is required.
3.2 Iterative Development
During the Iterative Development:
• The requirements are not clear from the user (customer).
• The structure of the software is pre-determined.
Testing of Iterative Development projects should concentrate only if the CASE (Computer Aided Software Engineering) tools are properly utilized and the functionality is thoroughly tested.
3.3 Maintenance System
The Maintenance System is where the structure of the program undergoes changes. The system is developed and being used, but it demands changes in the functional aspects of the system due to various reasons.
Testing Maintenance Systems requires structural testing. Top priority should be put into Regression Testing.
3.4 Purchased/Contracted Software
At times it may be required that you purchase software to integrate with your product or outsource the development of certain components of your product. This is Purchased or Contracted Software.
When you need to integrate third party software to your existing software, this demands the testing of the purchased software with your requirements. Since the two systems are designed and developed differently, the integration takes the top priority during testing. Also, Regression Testing of the integrated software is a must to cross check if the two software’s are working as per the requirements.
4. Types of Software Systems
The type of software system refers to the processing that will be performed by that system. This contains the following software system types.
4.1 Batch Systems
The Batch Systems are a set of programs that perform certain activities which do not require any input from the user.
A practical example is that when you are typing something on a word document, you press the key you require and the same is printed on the monitor. But processing (converting) the user input of the key to the machine understandable language, making the system understand what to be displayed and in return the word document displaying what you have typed is performed by the batch systems. These batch systems contain one or more Application Programming Interface (API) which perform various tasks.
4.2 Event Control Systems
Event Control Systems process real time data to provide the user with results for what command (s) he is given.
For example, when you type on the word document and press Ctrl + S, this tells the computer to save the document. How this is performed instantaneously? These real time command communications to the computer are provided by the Event Controls that are pre-defined in the system.
4.3 Process Control Systems
There are two or more different systems that communicate to provide the end user a specific utility. When two systems communicate, the co-ordination or data transfer becomes vital. Process Control Systems are the one’s which receive data from a different system and instructs the system which sent the data to perform specific tasks based on the reply sent by the system which received the data.
4.4 Procedure Control Systems
Procedure Control Systems are the one’s which control the functions of another system.
4.5 Advanced Mathematical Models
Systems, which make use of heavy mathematics, fall into the category of Mathematical Models. Usually all the computer software make use of mathematics in some way or the other. But, Advance Mathematical Models can be classified when there is heavy utilization of mathematics for performing certain actions. An example of Advanced Mathematical Model can be simulation systems which uses graphics and controls the positioning of software on the monitor or Decision and Strategy making software’s.
4.6 Message Processing Systems
A simple example is the SMS management software used by Mobile operator’s which handle incoming and outgoing messages. Another system, which is noteworthy is the system used by paging companies.
4.7 Diagnostic Software Systems
The Diagnostic Software System is one that helps in diagnosing the computer hardware components.
When you plug in a new device to your computer and start it, you can see the diagnostic software system doing some work. The “New Hardware Found” dialogue can be seen as a result of this system. Today, almost all the Operating System’s come packed with Diagnostic Software Systems.
4.8 Sensor and Signal Processing Systems
The message processing systems help in sending and receiving messages. The Sensor and Signal Processing Systems are more complex because these systems make use of mathematics for signal processing. In a signal processing system the computer receives input in the form of signals and then transforms the signals to a user understandable output.
4.9 Simulation Systems
A simulation system is a software application, some times used in combination with specialized hardware, which re-creates or simulates the complex behavior of a system in its real environment. It can be defined in many ways:
"The process of designing a model of a real system and conducting experiments with this model for the purpose of understanding the behavior of the system and/or evaluating various strategies for the operation of the system"-- Introduction to Simulation Using SIMAN, by C. D. Pegden, R. E. Shannon and R. P. Sadowski, McGraw-Hill, 1990.
“A simulation is a software package (sometimes bundled with special hardware input devices) that re-creates or simulates, albeit in a simplified manner, a complex phenomena, environment, or experience, providing the user with the opportunity for some new level of understanding. It is interactive, and usually grounded in some objective reality. A simulation is based on some underlying computational model of the phenomena, environment, or experience that it is simulating. (In fact, some authors use model and modeling as synonyms of simulation.)" --Kurt Schumaker, A Taxonomy of Simulation Software." Learning Technology Review.
In simple words simulation is nothing but a representation of a real system. In a programmable environment, simulations are used to study system behavior or test the system in an artificial environment that provides a limited representation of the real environment.
Why Simulation Systems
Simulation systems are easier, cheaper, and safer to use than real systems, and often the only way to build the real systems. For example, learning to fly a fighter plane using a simulator is much safer and less expensive than learning on a real fighter plane. System simulation mimics the operation of a real system such as the operation in a bank, or the running of the assembly line in a factory etc.
Simulation in the early stage of design cycle is important because the cost of mistakes increases dramatically later in the product life cycle. Also, simulation software can analyze the operation of a real system without the involvement of an expert, i.e. it can also be analyzed with a non-expert like a manager.
How to Build Simulation Systems
In order to create a simulation system we need a realistic model of the system behavior. One way of simulation is to create smaller versions of the real system.
The simulation system may use only software or a combination of software and hardware to model the real system. The simulation software often involves the integration of artificial intelligence and other modeling techniques.
What applications fall under this category?
Simulation is widely used in many fields. Some of the applications are:
• Models of planes and cars that are tested in wind tunnels to determine the aerodynamic properties.
• Used in computer Games (E.g. SimCity, car games etc). This simulates the working in a city, the roads, people talking, playing games etc.
• War tactics that are simulated using simulated battlefields.
• Most Embedded Systems are developed by simulation software before they ever make it to the chip fabrication labs.
• Stochastic simulation models are often used to model applications such as weather forecasting systems.
• Social simulation is used to model socio-economic situations.
• It is extensively used in the field of operations research.
What are the Characteristics of Simulation Systems?
Simulation Systems can be characterized in numerous ways depending on the characterization criteria applied. Some of them are listed below.
Deterministic Simulation Systems
Deterministic Simulation Systems have completely predictable outcomes. That is, given a certain input we can predict the exact outcome. Another feature of these systems is idempotency, which means that the results for any given input are always the same.
Examples include population prediction models, atmospheric science etc.
Stochastic Simulation Systems
Stochastic Simulation systems have models with random variables. This means that the exact outcome is not predictable for any given input, resulting in potentially very different outcomes for the same input.
Static Simulation Systems
Static Simulation systems use statistical models in which time does not play any role. These models include various probabilistic scenarios which are used to calculate the results of any given input. Examples of such systems include financial portfolio valuation models. The most common simulation technique used in these models is the Monte Carlo Simulation.
Dynamic Simulation Systems
A dynamic simulation system has a model that accommodates for changes in data over time. This means that the input data affecting the results will be entered into the simulation during its entire lifetime than just at the beginning. A simulation system used to predict the growth of the economy may need to incorporate changes in economic data, is a good example of a dynamic simulation system.
Discrete Simulation Systems
Discrete Simulation Systems use models that have discrete entities with multiple attributes. Each of these entities can be in any state, at any given time, represented by the values of its attributes. . The state of the system is a set of all the states of all its entities.
This state changes one discrete step at a time as events happens in the system. Therefore, the actual designing of the simulation involves making choices about which entities to model, what attributes represent the Entity State, what events to model, how these events impact the entity attributes, and the sequence of the events. Examples of these systems are simulated battlefield scenarios, highway traffic control systems, multiteller systems, computer networks etc.
Continuous Simulation Systems
If instead of using a model with discrete entities we use data with continuous values, we will end up with continuous simulation. For example instead of trying to simulate battlefield scenarios by using discrete entities such as soldiers and tanks, we can try to model behavior and movements of troops by using differential equations.
Social Simulation Systems
Social simulation is not a technique by itself but uses the various types of simulation described above. However, because of the specialized application of those techniques for social simulation it deserves a special mention of its own.
The field of social simulation involves using simulation to learn about and predict various social phenomenon such as voting patterns, migration patterns, economic decisions made by the general population, etc. One interesting application of social simulation is in a field called artificial life which is used to obtain useful insights into the formation and evolution of life.
What can be the possible test approach?
A simulation system’s primary responsibility is to replicate the behavior of the real system as accurately as possible. Therefore, a good place to start creating a test plan would be to understand the behavior of the real system.
Subjective Testing
Subjective testing mainly depends on an expert's opinion. An expert is a person who is proficient and experienced in the system under test. Conducting the test involves test runs of the simulation by the expert and then the expert evaluates and validates the results based on some criteria.
One advantage of this approach over objective testing is that it can test those conditions which cannot be tested objectively. For example, an expert can determine whether the joystick handling of the flight feels "right".
One disadvantage is that the evaluation of the system is based on the "expert's" opinion, which may differ from expert to expert. Also, if the system is very large then it is bound to have many experts. Each expert may view it differently and can give conflicting opinions. This makes it difficult to determine the validity of the system. Despite all these disadvantages, subjective testing is necessary for testing systems with human interaction.
Objective Testing
Objective testing is mainly used in systems where the data can be recorded while the simulation is running. This testing technique relies on the application of statistical and automated methods to the data collected.
Statistical methods are used to provide an insight into the accuracy of the simulation. These methods include hypothesis testing, data plots, principle component analysis and cluster analysis.
Automated testing requires a knowledge base of valid outcomes for various runs of simulation. This knowledge base is created by domain experts of the simulation system being tested. The data collected in various test runs is compared against this knowledge base to automatically validate the system under test. An advantage of this kind of testing is that the system can continually be regression tested as it is being developed.
Statistical Methods
Statistical methods are used to provide an insight into the accuracy of the simulation. These methods include hypothesis testing, data plots, principle component analysis and cluster analysis.
Automated Testing
Automated testing requires a knowledge base of valid outcomes for various runs of simulation. This knowledge base is created by domain experts of the simulation system being tested. The data collected in various test runs is compared against this knowledge base to automatically validate the system under test. An advantage of this kind of testing is that the system can continually be regression tested as it is being developed.
4.10 Database Management Systems
As the name denotes, the Database Management Systems (DBMS) handles the management of databases. It is basically a collection of programs that enable the storage, modification and extraction from the Database. The DBMS, as they are often referred to as, can be of various different types ranging from small systems that run on PC’s to Mainframe’s. The following can be categorized as example of DBMS:
• Computerized Library Systems.
• Automated Teller Machines.
• Passenger Reservation Systems.
• Inventory Systems.
4.11 Data Acquisition
Data Acquisition systems, taken in real time data and store them for future use. A simple example of Data Acquisition system can be a ATC (Air Traffic Control) Software which takes in real time data of the position and speed of the flight and stores it in compressed form for later use.
4.12 Data Presentation
Data Presentation software stores data and displays the same to the user when required. An example is a Content Management System. You have a web site and this is in English, you also have your web site in other languages. The user can select the language he wishes to see and the system displays the same web site in the user chosen language. You develop your web site in various languages and store them on the system. The system displays the required language, the user chooses.
4.13 Decision and Planning Systems
These systems use Artificial Intelligence techniques to provide decision-making solutions to the user.
4.14 Pattern and Image Processing Systems
These systems are used for scanning, storing, modifying and displaying graphic images. The use of such systems is now being increased as research tests are being conducted in visual modeling and their use in our daily lives is increasing. These systems are used for security requests such as diagnosing photograph, thumb impression of the visitor etc.
4.15 Computer System Software Systems
These are the normal computer software’s, that can be used for various purposes.
4.16 Software Development Tools
These systems ease the process of Software Development.
5. Heuristics of Software Testing
Testability
Software testability is how easily, completely and conveniently a computer program can be tested.
Software engineers design a computer product, system or program keeping in mind the product testability. Good programmers are willing to do things that will help the testing process and a checklist of possible design points, features and so on can be useful in negotiating with them.
Here are the two main heuristics of software testing.
1. Visibility
2. Control
Visibility
Visibility is our ability to observe the states and outputs of the software under test. Features to improve the visibility are
• Access to Code
Developers must provide full access (source code, infrastructure, etc) to testers. The Code, change records and design documents should be provided to the testing team. The testing team should read and understand the code.
• Event logging
The events to log include User events, System milestones, Error handling and completed transactions. The logs may be stored in files, ring buffers in memory, and/or serial ports. Things to be logged include description of event, timestamp, subsystem, resource usage and severity of event. Logging should be adjusted by subsystem and type. Log file report internal errors, help in isolating defects, and give useful information about context, tests, customer usage and test coverage.
The more readable the Log Reports are, the easier it becomes to identify the defect cause and work towards corrective measures.
• Error detection mechanisms
Data integrity checking and System level error detection (e.g. Microsoft Appviewer) are useful here. In addition, Assertions and probes with the following features are really helpful
Code is added to detect internal errors.
Assertions abort on error.
Probes log errors.
Design by Contract theory---This technique requires that assertions be defined for functions. Preconditions apply to input and violations implicate calling functions while post-conditions apply to outputs and violations implicate called functions. This effectively solves the oracle problem for testing.
• Resource Monitoring
Memory usage should be monitored to find memory leaks. States of running methods, threads or processes should be watched (Profiling interfaces may be used for this.). In addition, the configuration values should be dumped. Resource monitoring is of particular concern in applications where the load on the application in real time is estimated to be considerable.
Control
Control refers to our ability to provide inputs and reach states in the software under test.
The features to improve controllability are:
• Test Points
Allow data to be inspected, inserted or modified at points in the software. It is especially useful for dataflow applications. In addition, a pipe and filters architecture provides many opportunities for test points.
• Custom User Interface controls
Custom UI controls often raise serious testability problems with GUI test drivers. Ensuring testability usually requires:
Adding methods to report necessary information
Customizing test tools to make use of these methods
Getting a tool expert to advise developers on testability and to build the required support.
Asking third party control vendors regarding support by test tools.
• Test Interfaces
Interfaces may be provided specifically for testing e.g. Excel and Xconq etc.
Existing interfaces may be able to support significant testing e.g. InstallSheild, AutoCAD, Tivoli, etc.
• Fault injection
Error seeding---instrumenting low level I/O code to simulate errors---makes it much easier to test error handling. It can be handled at both system and application level, Tivoli, etc.
• Installation and setup
Testers should be notified when installation has completed successfully. They should be able to verify installation, programmatically create sample records and run multiple clients, daemons or servers on a single machine.
A BROADER VIEW
Below are given a broader set of characteristics (usually known as James Bach heuristics) that lead to testable software.
Categories of Heuristics of software testing
• Operability
The better it works, the more efficiently it can be tested.
The system should have few bugs, no bugs should block the execution of tests and the product should evolve in functional stages (simultaneous development and testing).
• Observability
What we see is what we test.
Distinct output should be generated for each input
Current and past system states and variables should be visible during testing
All factors affecting the output should be visible.
Incorrect output should be easily identified.
Source code should be easily accessible.
Internal errors should be automatically detected (through self-testing mechanisms) and reported.
• Controllability
The better we control the software, the more the testing process can be automated and optimized.
Check that
All outputs can be generated and code can be executed through some combination of input.
Software and hardware states can be controlled directly by the test engineer.
Inputs and output formats are consistent and structured.
Test can be conveniently, specified, automated and reproduced.
• Decomposability
By controlling the scope of testing, we can quickly isolate problems and perform effective and efficient testing.
The software system should be built from independent modules which can be tested independently.
• Simplicity
The less there is to test, the more quickly we can test it.
The points to consider in this regard are functional (e.g. minimum set of features), structural (e.g. architecture is modularized) and code (e.g. a coding standard is adopted) simplicity.
• Stability
The fewer the changes, the fewer are the disruptions to testing.
The changes to software should be infrequent, controlled and not invalidating existing tests. The software should be able to recover well from failures.
• Understandability
The more information we will have, the smarter we will test.
The testers should be able to understand well the design, changes to the design and the dependencies between internal, external and shared components.
Technical documentation should be instantly accessible, accurate, well organized, specific and detailed.
• Suitability
The more we know about the intended use of the software, the better we can organize our testing to find important bugs.
The above heuristics can be used by a software engineer to develop a software configuration (i.e. program, data and documentation) that is convenient to test and verify.
6. When Testing should occur?
Wrong Assumption
Testing is sometimes incorrectly thought as an after-the-fact activity; performed after programming is done for a product. Instead, testing should be performed at every development stage of the product .Test data sets must be derived and their correctness and consistency should be monitored throughout the development process. If we divide the lifecycle of software development into “Requirements Analysis”, “Design”, “Programming/Construction” and “Operation and Maintenance”, then testing should accompany each of the above phases. If testing is isolated as a single phase late in the cycle, errors in the problem statement or design may incur exorbitant costs. Not only must the original error be corrected, but the entire structure built upon it must also be changed. Therefore, testing should not be isolated as an inspection activity. Rather testing should be involved throughout the SDLC in order to bring out a quality product.
Testing Activities in Each Phase
The following testing activities should be performed during the phases
• Requirements Analysis - (1) Determine correctness (2) Generate functional test data.
• Design - (1) Determine correctness and consistency (2) Generate structural and functional test data.
• Programming/Construction - (1) Determine correctness and consistency (2) Generate structural and functional test data (3) Apply test data (4) Refine test data.
• Operation and Maintenance - (1) Retest.
Now we consider these in detail.
Requirements Analysis
The following test activities should be performed during this stage.
• Invest in analysis at the beginning of the project - Having a clear, concise and formal statement of the requirements facilitates programming, communication, error analysis an d test data generation.
The requirements statement should record the following information and decisions:
1. Program function - What the program must do?
2. The form, format, data types and units for input.
3. The form, format, data types and units for output.
4. How exceptions, errors and deviations are to be handled.
5. For scientific computations, the numerical method or at least the required accuracy of the solution.
6. The hardware/software environment required or assumed (e.g. the machine, the operating system, and the implementation language).
Deciding the above issues is one of the activities related to testing that should be performed during this stage.
• Start developing the test set at the requirements analysis phase - Data should be generated that can be used to determine whether the requirements have been met. To do this, the input domain should be partitioned into classes of values that the program will treat in a similar manner and for each class a representative element should be included in the test data. In addition, following should also be included in the data set: (1) boundary values (2) any non-extreme input values that would require special handling.
The output domain should be treated similarly.
Invalid input requires the same analysis as valid input.
• The correctness, consistency and completeness of the requirements should also be analyzed - Consider whether the correct problem is being solved, check for conflicts and inconsistencies among the requirements and consider the possibility of missing cases.
Design
The design document aids in programming, communication, and error analysis and test data generation. The requirements statement and the design document should together give the problem and the organization of the solution i.e. what the program will do and how it will be done.
The design document should contain:
• Principal data structures.
• Functions, algorithms, heuristics or special techniques used for processing.
• The program organization, how it will be modularized and categorized into external and internal interfaces.
• Any additional information.
Here the testing activities should consist of:
• Analysis of design to check its completeness and consistency - the total process should be analyzed to determine that no steps or special cases have been overlooked. Internal interfaces, I/O handling and data structures should specially be checked for inconsistencies.
• Analysis of design to check whether it satisfies the requirements - check whether both requirements and design document contain the same form, format, units used for input and output and also that all functions listed in the requirement document have been included in the design document. Selected test data which is generated during the requirements analysis phase should be manually simulated to determine whether the design will yield the expected values.
• Generation of test data based on the design - The tests generated should cover the structure as well as the internal functions of the design like the data structures, algorithm, functions, heuristics and general program structure etc. Standard extreme and special values should be included and expected output should be recorded in the test data.
• Reexamination and refinement of the test data set generated at the requirements analysis phase.
The first two steps should also be performed by some colleague and not only the designer/developer.
Programming/Construction
Here the main testing points are:
• Check the code for consistency with design - the areas to check include modular structure, module interfaces, data structures, functions, algorithms and I/O handling.
• Perform the Testing process in an organized and systematic manner with test runs dated, annotated and saved. A plan or schedule can be used as a checklist to help the programmer organize testing efforts. If errors are found and changes made to the program, all tests involving the erroneous segment (including those which resulted in success previously) must be rerun and recorded.
• Asks some colleague for assistance - Some independent party, other than the programmer of the specific part of the code, should analyze the development product at each phase. The programmer should explain the product to the party who will then question the logic and search for errors with a checklist to guide the search. This is needed to locate errors the programmer has overlooked.
• Use available tools - the programmer should be familiar with various compilers and interpreters available on the system for the implementation language being used because they differ in their error analysis and code generation capabilities.
• Apply Stress to the Program - Testing should exercise and stress the program structure, the data structures, the internal functions and the externally visible functions or functionality. Both valid and invalid data should be included in the test set.
• Test one at a time - Pieces of code, individual modules and small collections of modules should be exercised separately before they are integrated into the total program, one by one. Errors are easier to isolate when the no. of potential interactions should be kept small. Instrumentation-insertion of some code into the program solely to measure various program characteristics – can be useful here. A tester should perform array bound checks, check loop control variables, determine whether key data values are within permissible ranges, trace program execution, and count the no. of times a group of statements is executed.
• Measure testing coverage/When should testing stop? - If errors are still found every time the program is executed, testing should continue. Because errors tend to cluster, modules appearing particularly error-prone require special scrutiny.
The metrics used to measure testing thoroughness include statement testing (whether each statement in the program has been executed at least once), branch testing (whether each exit from each branch has been executed at least once) and path testing (whether all logical paths, which may involve repeated execution of various segments, have been executed at least once). Statement testing is the coverage metric most frequently used as it is relatively simple to implement.
The amount of testing depends on the cost of an error. Critical programs or functions require more thorough testing than the less significant functions.
Operations and maintenance
Corrections, modifications and extensions are bound to occur even for small programs and testing is required every time there is a change. Testing during maintenance is termed regression testing. The test set, the test plan, and the test results for the original program should exist. Modifications must be made to accommodate the program changes, and then all portions of the program affected by the modifications must be re-tested. After regression testing is complete, the program and test documentation must be updated to reflect the changes.
7. The Test Development Life Cycle (TDLC)
Usually, Testing is considered as a part of the System Development Life Cycle. With our practical experience, we framed this Test Development Life Cycle.
The diagram does not depict where and when you write your Test Plan and Strategy documents. But, it is understood that before you begin your testing activities these documents should be ready. Ideally, when the Project Plan and Project Strategy are being made, this is the time when the Test Plan and Test Strategy documents are also made.
Test Development Life Cycle (TDLC)
8. When should Testing stop?
"When to stop testing" is one of the most difficult questions to a test engineer.
The following are few of the common Test Stop criteria:
1. All the high priority bugs are fixed.
2. The rate at which bugs are found is too small.
3. The testing budget is exhausted.
4. The project duration is completed.
5. The risk in the project is under acceptable limit.
Practically, we feel that the decision of stopping testing is based on the level of the risk acceptable to the management. As testing is a never ending process we can never assume that 100 % testing has been done, we can only minimize the risk of shipping the product to client with X testing done. The risk can be measured by Risk analysis but for small duration / low budget / low resources project, risk can be deduced by simply: -
• Measuring Test Coverage.
• Number of test cycles.
• Number of high priority bugs.
9. Verification Strategies
What is ‘Verification’?
Verification is the process of evaluating a system or component to determine whether the products of a given development phase satisfy the conditions imposed at the start of that phase.
What is the importance of the Verification Phase?
Verification process helps in detecting defects early, and preventing their leakage downstream. Thus, the higher cost of later detection and rework is eliminated.
9.1 Review
A process or meeting during which a work product, or set of work products, is presented to project personnel, managers, users, customers, or other interested parties for comment or approval.
The main goal of reviews is to find defects. Reviews are a good compliment to testing to help assure quality. A few purposes’ of SQA reviews can be as follows:
• Assure the quality of deliverable’s before the project moves to the next stage.
• Once a deliverable has been reviewed, revised as required, and approved, it can be used as a basis for the next stage in the life cycle.
What are the various types of reviews?
Types of reviews include Management Reviews, Technical Reviews, Inspections, Walkthroughs and Audits.
Management Reviews
Management reviews are performed by those directly responsible for the system in order to monitor progress, determine status of plans and schedules, confirm requirements and their system allocation.
Therefore the main objectives of Management Reviews can be categorized as follows:
• Validate from a management perspective that the project is making progress according to the project plan.
• Ensure that deliverables are ready for management approvals.
• Resolve issues that require management’s attention.
• Identify any project bottlenecks.
• Keeping project in Control.
Support decisions made during such reviews include Corrective actions, Changes in the allocation of resources or changes to the scope of the project
In management reviews the following Software products are reviewed:
Audit Reports
Contingency plans
Installation plans
Risk management plans
Software Q/A
The participants of the review play the roles of Decision-Maker, Review Leader, Recorder, Management Staff, and Technical Staff.
Technical Reviews
Technical reviews confirm that product Conforms to specifications, adheres to regulations, standards, guidelines, plans, changes are properly implemented, changes affect only those system areas identified by the change specification.
The main objectives of Technical Reviews can be categorized as follows:
• Ensure that the software confirms to the organization standards.
• Ensure that any changes in the development procedures (design, coding, testing) are implemented per the organization pre-defined standards.
In technical reviews, the following Software products are reviewed
• Software requirements specification
• Software design description
• Software test documentation
• Software user documentation
• Installation procedure
• Release notes
The participants of the review play the roles of Decision-maker, Review leader, Recorder, Technical staff.
What is Requirement Review?
A process or meeting during which the requirements for a system, hardware item, or software item are presented to project personnel, managers, users, customers, or other interested parties for comment or approval. Types include system requirements review, software requirements review.
Who is involved in Requirement Review?
• Product management leads Requirement Review. Members from every affected department participates in the review
Input Criteria
Software requirement specification is the essential document for the review. A checklist can be used for the review.
Exit Criteria
Exit criteria include the filled & completed checklist with the reviewers’ comments & suggestions and the re-verification whether they are incorporated in the documents.
What is Design Review?
A process or meeting during which a system, hardware, or software design is presented to project personnel, managers, users, customers, or other interested parties for comment or approval. Types include critical design review, preliminary design review, and system design review.
Who involve in Design Review?
• QA team member leads design review. Members from development team and QA team participate in the review.
Input Criteria
Design document is the essential document for the review. A checklist can be used for the review.
Exit Criteria
Exit criteria include the filled & completed checklist with the reviewers’ comments & suggestions and the re-verification whether they are incorporated in the documents.
What is Code Review?
A meeting at which software code is presented to project personnel, managers, users, customers, or other interested parties for comment or approval.
Who is involved in Code Review?
• QA team member (In case the QA Team is only involved in Black Box Testing, then the Development team lead chairs the review team) leads code review. Members from development team and QA team participate in the review.
Input Criteria
The Coding Standards Document and the Source file are the essential documents for the review. A checklist can be used for the review.
Exit Criteria
Exit criteria include the filled & completed checklist with the reviewers’ comments & suggestions and the re-verification whether they are incorporated in the documents.
9.2 Walkthrough
A static analysis technique in which a designer or programmer leads members of the development team and other interested parties through a segment of documentation or code, and the participants ask questions and make comments about possible errors, violation of development standards, and other problems.
The objectives of Walkthrough can be summarized as follows:
• Detect errors early.
• Ensure (re)established standards are followed:
• Train and exchange technical information among project teams which participate in the walkthrough.
• Increase the quality of the project, thereby improving morale of the team members.
The participants in Walkthroughs assume one or more of the following roles:
a) Walk-through leader
b) Recorder
c) Author
d) Team member
To consider a review as a systematic walk-through, a team of at least two members shall be assembled. Roles may be shared among the team members. The walk-through leader or the author may serve as the recorder. The walk-through leader may be the author.
Individuals holding management positions over any member of the walk-through team shall not participate in the walk-through.
Input to the walk-through shall include the following:
a) A statement of objectives for the walk-through
b) The software product being examined
c) Standards that are in effect for the acquisition, supply, development, operation, and/or maintenance of the software product
Input to the walk-through may also include the following:
d) Any regulations, standards, guidelines, plans, and procedures against which the software product is to be inspected
e) Anomaly categories
The walk-through shall be considered complete when
a) The entire software product has been examined
b) Recommendations and required actions have been recorded
c) The walk-through output has been completed
9.3 Inspection
A static analysis technique that relies on visual examination of development products to detect errors, violations of development standards, and other problems. Types include code inspection; design inspection, Architectural inspections, Test ware inspections etc.
The participants in Inspections assume one or more of the following roles:
a) Inspection leader
b) Recorder
c) Reader
d) Author
e) Inspector
All participants in the review are inspectors. The author shall not act as inspection leader and should not act as reader or recorder. Other roles may be shared among the team members. Individual participants may act in more than one role.
Individuals holding management positions over any member of the inspection team shall not participate in the inspection.
Input to the inspection shall include the following:
a) A statement of objectives for the inspection
b) The software product to be inspected
c) Documented inspection procedure
d) Inspection reporting forms
e) Current anomalies or issues list
Input to the inspection may also include the following:
f) Inspection checklists
g) Any regulations, standards, guidelines, plans, and procedures against which the software product is to be inspected
h) Hardware product specifications
i) Hardware performance data
j) Anomaly categories
The individuals may make additional reference material available responsible for the software product when requested by the inspection leader.
The purpose of the exit criteria is to bring an unambiguous closure to the inspection meeting. The exit decision shall determine if the software product meets the inspection exit criteria and shall prescribe any appropriate rework and verification. Specifically, the inspection team shall identify the software product disposition as one of the following:
a) Accept with no or minor rework. The software product is accepted as is or with only minor rework. (For example, that would require no further verification).
b) Accept with rework verification. The software product is to be accepted after the inspection leader or
a designated member of the inspection team (other than the author) verifies rework.
c) Re-inspect. Schedule a re-inspection to verify rework. At a minimum, a re-inspection shall examine the software product areas changed to resolve anomalies identified in the last inspection, as well as side effects of those changes.
10. Testing Types and Techniques
Testing types
Testing types refer to different approaches towards testing a computer program, system or product. The two types of testing are black box testing and white box testing, which would both be discussed in detail in this chapter. Another type, termed as gray
box testing or hybrid testing is evolving presently and it combines the features of the two types.
Testing Techniques
Testing techniques refer to different methods of testing particular features a computer program, system or product. Each testing type has its own testing techniques while some techniques combine the feature of both types. Some techniques are
• Error and anomaly detection technique
• Interface checking
• Physical units checking
• Loop testing ( Discussed in detail in this chapter)
• Basis Path testing/McCabe’s cyclomatic number( Discussed in detail in this chapter)
• Control structure testing( Discussed in detail in this chapter)
• Error Guessing( Discussed in detail in this chapter)
• Boundary Value analysis ( Discussed in detail in this chapter)
• Graph based testing( Discussed in detail in this chapter)
• Equivalence partitioning( Discussed in detail in this chapter)
• Instrumentation based testing
• Random testing
• Domain testing
• Halstead’s software science
• And many more
Some of these and many others would be discussed in the later sections of this chapter.
Difference between Testing Types and Testing Techniques
Testing types deal with what aspect of the computer software would be tested, while testing techniques deal with how a specific part of the software would be tested.
That is, testing types mean whether we are testing the function or the structure of the software. In other words, we may test each function of the software to see if it is operational or we may test the internal components of the software to check if its internal workings are according to specification.
On the other hand, ‘Testing technique’ means what methods or ways would be applied or calculations would be done to test a particular feature of a software (Sometimes we test the interfaces, sometimes we test the segments, sometimes loops etc.)
How to Choose a Black Box or White Box Test?
White box testing is concerned only with testing the software product; it cannot guarantee that the complete specification has been implemented. Black box testing is concerned only with testing the specification; it cannot guarantee that all parts of the implementation have been tested. Thus black box testing is testing against the specification and will discover faults of omission, indicating that part of the specification has not been fulfilled. White box testing is testing against the implementation and will discover faults of commission, indicating that part of the implementation is faulty. In order to completely test a software product both black and white box testing are required.
White box testing is much more expensive (In terms of resources and time) than black box testing. It requires the source code to be produced before the tests can be planned and is much more laborious in the determination of suitable input data and the determination if the software is or is not correct. It is advised to start test planning with a black box testing approach as soon as the specification is available. White box tests are to be planned as soon as the Low Level Design (LLD) is complete. The Low Level Design will address all the algorithms and coding style. The paths should then be checked against the black box test plan and any additional required test cases should be determined and applied.
The consequences of test failure at initiative/requirements stage are very expensive. A failure of a test case may result in a change, which requires all black box testing to be repeated and the re-determination of the white box paths. The cheaper option is to regard the process of testing as one of quality assurance rather than quality control. The intention is that sufficient quality is put into all previous design and production stages so that it can be expected that testing will project the presence of very few faults, rather than testing being relied upon to discover any faults in the software, as in case of quality control. A combination of black box and white box test considerations is still not a completely adequate test rationale.
10.1 White Box Testing
What is WBT?
White box testing involves looking at the structure of the code. When you know the internal structure of a product, tests can be conducted to ensure that the internal operations performed according to the specification. And all internal components have been adequately exercised. In other word WBT tends to involve the coverage of the specification in the code.
Code coverage is defined in six types as listed below.
• Segment coverage – Each segment of code b/w control structure is executed at least once.
• Branch Coverage or Node Testing – Each branch in the code is taken in each possible direction at least once.
• Compound Condition Coverage – When there are multiple conditions, you must test not only each direction but also each possible combinations of conditions, which is usually done by using a ‘Truth Table’
• Basis Path Testing – Each independent path through the code is taken in a pre-determined order. This point will further be discussed in other section.
• Data Flow Testing (DFT) – In this approach you track the specific variables through each possible calculation, thus defining the set of intermediate paths through the code i.e., those based on each piece of code chosen to be tracked. Even though the paths are considered independent, dependencies across multiple paths are not really tested for by this approach. DFT tends to reflect dependencies but it is mainly through sequences of data manipulation. This approach tends to uncover bugs like variables used but not initialize, or declared but not used, and so on.
• Path Testing – Path testing is where all possible paths through the code are defined and covered. This testing is extremely laborious and time consuming.
• Loop Testing – In addition top above measures, there are testing strategies based on loop testing. These strategies relate to testing single loops, concatenated loops, and nested loops. Loops are fairly simple to test unless dependencies exist among the loop or b/w a loop and the code it contains.
What do we do in WBT?
In WBT, we use the control structure of the procedural design to derive test cases. Using WBT methods a tester can derive the test cases that
• Guarantee that all independent paths within a module have been exercised at least once.
• Exercise all logical decisions on their true and false values.
• Execute all loops at their boundaries and within their operational bounds
• Exercise internal data structures to ensure their validity.
White box testing (WBT) is also called Structural or Glass box testing.
Why WBT?
We do WBT because Black box testing is unlikely to uncover numerous sorts of defects in the program. These defects can be of the following nature:
• Logic errors and incorrect assumptions are inversely proportional to the probability that a program path will be executed. Error tend to creep into our work when we design and implement functions, conditions or controls that are out of the program
• The logical flow of the program is sometimes counterintuitive, meaning that our unconscious assumptions about flow of control and data may lead to design errors that are uncovered only when path testing starts.
• Typographical errors are random, some of which will be uncovered by syntax checking mechanisms but others will go undetected until testing begins.
Skills Required
Talking theoretically, all we need to do in WBT is to define all logical paths, develop test cases to exercise them and evaluate results i.e. generate test cases to exercise the program logic exhaustively.
For this we need to know the program well i.e. We should know the specification and the code to be tested; related documents should be available too us .We must be able to tell the expected status of the program versus the actual status found at any point during the testing process.
Limitations
Unfortunately in WBT, exhaustive testing of a code presents certain logistical problems. Even for small programs, the number of possible logical paths can be very large. For instance, a 100 line C Language program that contains two nested loops executing 1 to 20 times depending upon some initial input after some basic data declaration. Inside the interior loop four if-then-else constructs are required. Then there are approximately 1014 logical paths that are to be exercised to test the program exhaustively. Which means that a magic test processor developing a single test case, execute it and evaluate results in one millisecond would require 3170 years working continuously for this exhaustive testing which is certainly impractical. Exhaustive WBT is impossible for large software systems. But that doesn’t mean WBT should be considered as impractical. Limited WBT in which a limited no. of important logical paths are selected and exercised and important data structures are probed for validity, is both practical and WBT. It is suggested that white and black box testing techniques can be coupled to provide an approach that that validates the software interface selectively ensuring the correction of internal working of the software.
Tools used for White Box testing:
Few Test automation tool vendors offer white box testing tools which:
1) Provide run-time error and memory leak detection;
2) Record the exact amount of time the application spends in any given block of code for the purpose of finding inefficient code bottlenecks; and
3) Pinpoint areas of the application that have and have not been executed.
10.1.1 Basis Path Testing
Basis path testing is a white box testing technique first proposed by Tom McCabe. The Basis path method enables to derive a logical complexity measure of a procedural design and use this measure as a guide for defining a basis set of execution paths. Test Cases derived to exercise the basis set are guaranteed to execute every statement in the program at least one time during testing.
10.1.2 Flow Graph Notation
The flow graph depicts logical control flow using a diagrammatic notation. Each structured construct has a corresponding flow graph symbol.
10.1.3 Cyclomatic Complexity
Cyclomatic complexity is a software metric that provides a quantitative measure of the logical complexity of a program. When used in the context of a basis path testing method, the value computed for Cyclomatic complexity defines the number for independent paths in the basis set of a program and provides us an upper bound for the number of tests that must be conducted to ensure that all statements have been executed at least once.
An independent path is any path through the program that introduces at least one new set of processing statements or a new condition.
Computing Cyclomatic Complexity
Cyclomatic complexity has a foundation in graph theory and provides us with extremely useful software metric. Complexity is computed in one of the three ways:
1. The number of regions of the flow graph corresponds to the Cyclomatic complexity.
2. Cyclomatic complexity, V(G), for a flow graph, G is defined as
V (G) = E-N+2
Where E, is the number of flow graph edges, N is the number of flow graph nodes.
3. Cyclomatic complexity, V (G) for a flow graph, G is also defined as:
V (G) = P+1
Where P is the number of predicate nodes contained in the flow graph G.
10.1.4 Graph Matrices
The procedure for deriving the flow graph and even determining a set of basis paths is amenable to mechanization. To develop a software tool that assists in basis path testing, a data structure, called a graph matrix can be quite useful.
A Graph Matrix is a square matrix whose size is equal to the number of nodes on the flow graph. Each row and column corresponds to an identified node, and matrix entries correspond to connections between nodes.
10.1.5 Control Structure Testing
Described below are some of the variations of Control Structure Testing.
Condition Testing
Condition testing is a test case design method that exercises the logical conditions contained in a program module.
Data Flow Testing
The data flow testing method selects test paths of a program according to the locations of definitions and uses of variables in the program.
10.1.6 Loop Testing
Loop Testing is a white box testing technique that focuses exclusively on the validity of loop constructs. Four classes of loops can be defined: Simple loops, Concatenated loops, nested loops, and unstructured loops.
Simple Loops
The following sets of tests can be applied to simple loops, where ‘n’ is the maximum number of allowable passes through the loop.
1. Skip the loop entirely.
2. Only one pass through the loop.
3. Two passes through the loop.
4. ‘m’ passes through the loop where m
5. n-1, n, n+1 passes through the loop.
Nested Loops
If we extend the test approach from simple loops to nested loops, the number of possible tests would grow geometrically as the level of nesting increases.
1. Start at the innermost loop. Set all other loops to minimum values.
2. Conduct simple loop tests for the innermost loop while holding the outer loops at their minimum iteration parameter values. Add other tests for out-of-range or exclude values.
3. Work outward, conducting tests for the next loop, but keep all other outer loops at minimum values and other nested loops to “typical” values.
4. Continue until all loops have been tested.
Concatenated Loops
Concatenated loops can be tested using the approach defined for simple loops, if each of the loops is independent of the other. However, if two loops are concatenated and the loop counter for loop 1 is used as the initial value for loop 2, then the loops are not independent.
Unstructured Loops
Whenever possible, this class of loops should be redesigned to reflect the use of the structured programming constructs.
10.2 Black Box Testing
Black box is a test design method. Black box testing treats the system as a "black-box", so it doesn't explicitly use Knowledge of the internal structure. Or in other words the Test engineer need not know the internal working of the “Black box”.
It focuses on the functionality part of the module.
Some people like to call black box testing as behavioral, functional, opaque-box, and closed-box. While the term black box is most popularly use, many people prefer the terms "behavioral" and "structural" for black box and white box respectively. Behavioral test design is slightly different from black-box test design because the use of internal knowledge isn't strictly forbidden, but it's still discouraged.
Personally we feel that there is a trade off between the approaches used to test a product using white box and black box types.
There are some bugs that cannot be found using only black box or only white box. If the test cases are extensive and the test inputs are also from a large sample space then it is always possible to find majority of the bugs through black box testing.
Tools used for Black Box testing:
Many tool vendors have been producing tools for automated black box and automated white box testing for several years. The basic functional or regression testing tools capture the results of black box tests in a script format. Once captured, these scripts can be executed against future builds of an application to verify that new functionality hasn't disabled previous functionality.
Advantages of Black Box Testing
- Tester can be non-technical.
- This testing is most likely to find those bugs as the user would find.
- Testing helps to identify the vagueness and contradiction in functional specifications.
- Test cases can be designed as soon as the functional specifications are complete
Disadvantages of Black Box Testing
- Chances of having repetition of tests that are already done by programmer.
- The test inputs needs to be from large sample space.
- It is difficult to identify all possible inputs in limited testing time. So writing test cases is slow and difficult
Chances of having unidentified paths during this testing
10.2.1 Graph Based Testing Methods
Software testing begins by creating a graph of important objects and their relationships and then devising a series of tests that will cover the graph so that each objects and their relationships and then devising a series of tests that will cover the graph so that each object and relationship is exercised and error is uncovered.
10.2.2 Error Guessing
Error Guessing comes with experience with the technology and the project. Error Guessing is the art of guessing where errors can be hidden. There are no specific tools and techniques for this, but you can write test cases depending on the situation: Either when reading the functional documents or when you are testing and find an error that you have not documented.
10.2.3 Boundary Value Analysis
Boundary Value Analysis (BVA) is a test data selection technique (Functional Testing technique) where the extreme values are chosen. Boundary values include maximum, minimum, just inside/outside boundaries, typical values, and error values. The hope is that, if a system works correctly for these special values then it will work correctly for all values in between.
Extends equivalence partitioning
Test both sides of each boundary
Look at output boundaries for test cases too
Test min, min-1, max, max+1, typical values
BVA focuses on the boundary of the input space to identify test cases
Rational is that errors tend to occur near the extreme values of an input variable
There are two ways to generalize the BVA techniques:
1. By the number of variables
o For n variables: BVA yields 4n + 1 test cases.
2. By the kinds of ranges
o Generalizing ranges depends on the nature or type of variables
NextDate has a variable Month and the range could be defined as {Jan, Feb, …Dec}
Min = Jan, Min +1 = Feb, etc.
Triangle had a declared range of {1, 20,000}
Boolean variables have extreme values True and False but there is no clear choice for the remaining three values
Advantages of Boundary Value Analysis
1. Robustness Testing - Boundary Value Analysis plus values that go beyond the limits
2. Min - 1, Min, Min +1, Nom, Max -1, Max, Max +1
3. Forces attention to exception handling
4. For strongly typed languages robust testing results in run-time errors that abort normal execution
Limitations of Boundary Value Analysis
BVA works best when the program is a function of several independent variables that represent bounded physical quantities
1. Independent Variables
o NextDate test cases derived from BVA would be inadequate: focusing on the boundary would not leave emphasis on February or leap years
o Dependencies exist with NextDate's Day, Month and Year
o Test cases derived without consideration of the function
2. Physical Quantities
o An example of physical variables being tested, telephone numbers - what faults might be revealed by numbers of 000-0000, 000-0001, 555-5555, 999-9998, 999-9999?
10.2.4 Equivalence Partitioning
Equivalence partitioning is a black box testing method that divides the input domain of a program into classes of data from which test cases can be derived.
EP can be defined according to the following guidelines:
1. If an input condition specifies a range, one valid and one two invalid classes are defined.
2. If an input condition requires a specific value, one valid and two invalid equivalence classes are defined.
3. If an input condition specifies a member of a set, one valid and one invalid equivalence class is defined.
4. If an input condition is Boolean, one valid and one invalid class is defined.
10.2.5 Comparison Testing
There are situations where independent versions of software be developed for critical applications, even when only a single version will be used in the delivered computer based system. It is these independent versions which form the basis of a black box testing technique called Comparison testing or back-to-back testing.
10.2.6 Orthogonal Array Testing
The Orthogonal Array Testing Strategy (OATS) is a systematic, statistical way of testing pair-wise interactions by deriving a suitable small set of test cases (from a large number of possibilities).
11. Designing Test Cases
There are various techniques in which you can design test cases. For example, the below illustrated gives you an overview as to how you derive test cases using the basis path method:
The basis path testing method can be applied to a procedural design or to source code. The following steps can be applied to derive the basis set:
1. Use the design or code as a foundation, draw corresponding flow graph.
2. Determine the Cyclomatic complexity of the resultant flow graph.
3. Determine a basis set of linearly independent paths.
4. Prepare test cases that will fore execution of each path in the basis set.
Let us now see how to design test cases in a generic manner:
1. Understand the requirements document.
2. Break the requirements into smaller requirements (if it improves your testability).
3. For each Requirement, decide what technique you should use to derive the test cases. For example, if you are testing a Login page, you need to write test cases basing on error guessing and also negative cases for handling failures.
4. Have a Traceability Matrix as follows:
Requirement No (In RD) Requirement Test Case No
What this Traceability Matrix provides you is the coverage of Testing. Keep filling in the Traceability matrix when you complete writing test case’s for each requirement.
12. Validation Phase
The Validation Phase falls into picture after the software is ready or when the code is being written. There are various techniques and testing types that can be appropriately used while performing the testing activities. Let us examine a few of them.
12.1 Unit Testing
This is a typical scenario of Manual Unit Testing activity-
A Unit is allocated to a Programmer for programming. Programmer has to use ‘Functional Specifications’ document as input for his work.
Programmer prepares ‘Program Specifications’ for his Unit from the Functional Specifications. Program Specifications describe the programming approach, coding tips for the Unit’s coding.
Using these ‘Program specifications’ as input, Programmer prepares ‘Unit Test Cases’ document for that particular Unit. A ‘Unit Test Cases Checklist’ may be used to check the completeness of Unit Test Cases document.
‘Program Specifications’ and ‘Unit Test Cases’ are reviewed and approved by Quality Assurance Analyst or by peer programmer.
The programmer implements some functionality for the system to be developed. The same is tested by referring the unit test cases. While testing that functionality if any defects have been found, they are recorded using the defect logging tool whichever is applicable. The programmer fixes the bugs found and tests the same for any errors.
Stubs and Drivers
A software application is made up of a number of ‘Units’, where output of one ‘Unit’ goes as an ‘Input’ of another Unit. e.g. A ‘Sales Order Printing’ program takes a ‘Sales Order’ as an input, which is actually an output of ‘Sales Order Creation’ program.
Due to such interfaces, independent testing of a Unit becomes impossible. But that is what we want to do; we want to test a Unit in isolation! So here we use ‘Stub’ and ‘Driver.
A ‘Driver’ is a piece of software that drives (invokes) the Unit being tested. A driver creates necessary ‘Inputs’ required for the Unit and then invokes the Unit.
A Unit may reference another Unit in its logic. A ‘Stub’ takes place of such subordinate unit during the Unit Testing. A ‘Stub’ is a piece of software that works similar to a unit which is referenced by the Unit being tested, but it is much simpler that the actual unit. A Stub works as a ‘Stand-in’ for the subordinate unit and provides the minimum required behavior for that unit.
Programmer needs to create such ‘Drivers’ and ‘Stubs’ for carrying out Unit Testing.
Both the Driver and the Stub are kept at a minimum level of complexity, so that they do not induce any errors while testing the Unit in question.
Example - For Unit Testing of ‘Sales Order Printing’ program, a ‘Driver’ program will have the code which will create Sales Order records using hardcoded data and then call ‘Sales Order Printing’ program. Suppose this printing program uses another unit which calculates Sales discounts by some complex calculations. Then call to this unit will be replaced by a ‘Stub’, which will simply return fix discount data.
Unit Test Cases
It must be clear by now that preparing Unit Test Cases document (referred to as UTC hereafter) is an important task in Unit Testing activity. Having an UTC, which is complete with every possible test case, leads to complete Unit Testing and thus gives an assurance of defect-free Unit at the end of Unit Testing stage. So let us discuss about how to prepare a UTC.
Think of following aspects while preparing Unit Test Cases –
Expected Functionality: Write test cases against each functionality that is expected to be provided from the Unit being developed.
e.g. If an SQL script contains commands for creating one table and altering another table then test cases should be written for testing creation of one table and alteration of another.
It is important that User Requirements should be traceable to Functional Specifications, Functional Specifications be traceable to Program Specifications and Program Specifications be traceable to Unit Test Cases. Maintaining such traceability ensures that the application fulfills User Requirements.
Input values:
o Every input value: Write test cases for each of the inputs accepted by the Unit.
e.g. If a Data Entry Form has 10 fields on it, write test cases for all 10 fields.
o Validation of input: Every input has certain validation rule associated with it. Write test cases to validate this rule. Also, there can be cross-field validations in which one field is enabled depending upon input of another field. Test cases for these should not be missed.
e.g. A combo box or list box has a valid set of values associated with it.
A numeric field may accept only positive values.
An email address field must have ampersand (@) and period (.) in it.
A ‘Sales tax code’ entered by user must belong to the ‘State’ specified by the user.
o Boundary conditions: Inputs often have minimum and maximum possible values. Do not forget to write test cases for them.
e.g. A field that accepts ‘percentage’ on a Data Entry Form should be able to accept inputs only from 1 to 100.
o Limitations of data types: Variables that hold the data have their value limits depending upon their data types. In case of computed fields, it is very important to write cases to arrive at an upper limit value of the variables.
o Computations: If any calculations are involved in the processing, write test cases to check the arithmetic expressions with all possible combinations of values.
Output values: Write test cases to generate scenarios, which will produce all types of output values that are expected from the Unit.
e.g. A Report can display one set of data if user chooses a particular option and another set of data if user chooses a different option. Write test cases to check each of these outputs. When the output is a result of some calculations being performed or some formulae being used, then approximations play a major role and must be checked.
Screen / Report Layout: Screen Layout or web page layout and Report layout must be tested against the requirements. It should not happen that the screen or the report looks beautiful and perfect, but user wanted something entirely different! It should ensure that pages and screens are consistent.
Path coverage: A Unit may have conditional processing which results in various paths the control can traverse through. Test case must be written for each of these paths.
Assumptions: A Unit may assume certain things for it to function. For example, a Unit may need a database to be open. Then test case must be written to check that the Unit reports error if such assumptions are not met.
Transactions: In case of database applications, it is important to make sure that transactions are properly designed and no way inconsistent data gets saved in the database.
Abnormal terminations: Behavior of the Unit in case of abnormal termination should be tested.
Error messages: Error messages should be short, precise and self-explanatory. They should be properly phrased and should be free of grammatical mistakes.
UTC Document
Given below is a simple format for UTC document.
Test Case No. Test Case purpose Procedure Expected Result Actual result
ID which can be referred to in other documents like ‘Traceability Matrix’, Root Cause Analysis of Defects etc. What to test How to test What should happen What actually happened?
This column can be omitted when Defect Recording Tool is used.
Note that as this is a sample, we have not provided columns for Pass/Fail and Remarks.
Example:
Let us say we want to write UTC for a Data Entry Form below:
Given below are some of the Unit Test Cases for the above Form:
Test Case No. Test Case purpose Procedure Expected Result Actual result
1 Item no. to start by ‘A’ or ‘B’. 1.Create a new record.
2.Type Item no. starting with ‘A’.
3.Type item no. starting with ‘B’.
4.Type item no. starting with any character other than ‘A’ and ‘B’. 2,3. Should get accepted and control should move to next field.
4. Should not get accepted. An error message should be displayed and control should remain in Item no. field.
2. Item Price to be between 1000 to 2000 if Item no. starts with ‘A’. 1.Create a new record with Item no. starting with ‘A’.
2.Specify price < 1000
3.Specify price >2000.
4.Specify price = 1000.
5.Specify price = 2000.
6.Specify price between 1000 and 2000. 2,3.Error should get displayed and control should remain in Price field.
4,5,6.Should get accepted and control should move to next field.
UTC Checklist
UTC checklist may be used while reviewing the UTC prepared by the programmer. As any other checklist, it contains a list of questions, which can be answered as either a ‘Yes’ or a ‘No’. The ‘Aspects’ list given in Section 4.3 above can be referred to while preparing UTC checklist.
e.g. Given below are some of the checkpoints in UTC checklist –
1. Are test cases present for all form field validations?
2. Are boundary conditions considered?
3. Are Error messages properly phrased?
Defect Recording
Defect Recording can be done on the same document of UTC, in the column of ‘Expected Results’. This column can be duplicated for the next iterations of Unit Testing.
Defect Recording can also be done using some tools like Bugzilla, in which defects are stored in the database.
Defect Recording needs to be done with care. It should be able to indicate the problem in clear, unambiguous manner, and reproducing of the defects should be easily possible from the defect information.
Conclusion
Exhaustive Unit Testing filters out the defects at an early stage in the Development Life Cycle. It proves to be cost effective and improves Quality of the Software before the smaller pieces are put together to form an application as a whole. Unit Testing should be done sincerely and meticulously, the efforts are paid well in the long run.
12.2 Integration Testing
Integration testing is a systematic technique for constructing the program structure while at the same time conducting tests to uncover errors associated with interfacing. The objective is to take unit tested components and build a program structure that has been dictated by design.
Usually, the following methods of Integration testing are followed:
1. Top-down Integration approach.
2. Bottom-up Integration approach.
12.2.1 Top-Down Integration
Top-down integration testing is an incremental approach to construction of program structure. Modules are integrated by moving downward through the control hierarchy, beginning with the main control module. Modules subordinate to the main control module are incorporated into the structure in either a depth-first or breadth-first manner.
1. The Integration process is performed in a series of five steps:
2. The main control module is used as a test driver and stubs are substituted for all components directly subordinate to the main control module.
3. Depending on the integration approach selected subordinate stubs are replaced one at a time with actual components.
4. Tests are conducted as each component is integrated.
5. On completion of each set of tests, stub is replaced with the real component.
6. Regression testing may be conducted to ensure that new errors have not been introduced.
12.2.2 Bottom-Up Integration
Bottom-up integration testing begins construction and testing with atomic modules (i.e. components at the lowest levels in the program structure). Because components are integrated from the bottom up, processing required for components subordinate to a given level is always available and the need for stubs is eliminated.
1. A Bottom-up integration strategy may be implemented with the following steps:
2. Low level components are combined into clusters that perform a specific software sub function.
3. A driver is written to coordinate test case input and output.
4. The cluster is tested.
Drivers are removed and clusters are combined moving upward in the program structure.
12.3 System Testing
System testing concentrates on testing the complete system with a variety of techniques and methods. System Testing comes into picture after the Unit and Integration Tests.
12.3.1 Compatibility Testing
Compatibility Testing concentrates on testing whether the given application goes well with third party tools, software or hardware platform.
For example, you have developed a web application. The major compatibility issue is, the web site should work well in various browsers. Similarly when you develop applications on one platform, you need to check if the application works on other operating systems as well. This is the main goal of Compatibility Testing.
Before you begin compatibility tests, our sincere suggestion is that you should have a cross reference matrix between various software’s, hardware based on the application requirements. For example, let us suppose you are testing a web application. A sample list can be as follows:
Hardware Software Operating System
Pentium – II, 128 MB RAM IE 4.x, Opera, Netscape Windows 95
Pentium – III, 256 MB RAM IE 5.x, Netscape Windows XP
Pentium – IV, 512 MB RAM Mozilla Linux
Compatibility tests are also performed for various client/server based applications where the hardware changes from client to client.
Compatibility Testing is very crucial to organizations developing their own products. The products have to be checked for compliance with the competitors of the third party tools, hardware, or software platform. E.g. A Call center product has been built for a solution with X product but there is a client interested in using it with Y product; then the issue of compatibility arises. It is of importance that the product is compatible with varying platforms. Within the same platform, the organization has to be watchful that with each new release the product has to be tested for compatibility.
A good way to keep up with this would be to have a few resources assigned along with their routine tasks to keep updated about such compatibility issues and plan for testing when and if the need arises.
By the above example it is not intended that companies which are not developing products do not have to cater for this type of testing. There case is equally existent, if an application uses standard software then would it be able to run successfully with the newer versions too? Or if a website is running on IE or Netscape, what will happen when it is opened through Opera or Mozilla. Here again it is best to keep these issues in mind and plan for compatibility testing in parallel to avoid any catastrophic failures and delays.
12.3.2 Recovery Testing
Recovery testing is a system test that focuses the software to fall in a variety of ways and verifies that recovery is properly performed. If it is automatic recovery then re-initialization, check pointing mechanisms, data recovery and restart should be evaluated for correctness. If recovery requires human intervention, the mean-time-to-repair (MTTR) is evaluated to determine whether it is within acceptable limits.
12.3.3 Usability Testing
Usability is the degree to which a user can easily learn and use a product to achieve a goal. Usability testing is the system testing which attempts to find any human-factor problems. A simpler description is testing the software from a users’ point of view. Essentially it means testing software to prove/ensure that it is user-friendly, as distinct from testing the functionality of the software. In practical terms it includes ergonomic considerations, screen design, standardization etc.
The idea behind usability testing is to have actual users perform the tasks for which the product was designed. If they can't do the tasks or if they have difficulty performing the tasks, the UI is not adequate and should be redesigned. It should be remembered that usability testing is just one of the many techniques that serve as a basis for evaluating the UI in a user-centered approach. Other techniques for evaluating a UI include inspection methods such as heuristic evaluations, expert reviews, card-sorting, matching test or Icon intuitiveness evaluation, cognitive walkthroughs. Confusion regarding usage of the term can be avoided if we use ‘usability evaluation’ for the generic term and reserve ‘usability testing’ for the specific evaluation method based on user performance. Heuristic Evaluation and Usability Inspection or cognitive walkthrough does not involve real users.
It often involves building prototypes of parts of the user interface, having representative users perform representative tasks and seeing if the appropriate users can perform the tasks. In other techniques such as the inspection methods, it is not performance, but someone's opinion of how users might perform that is offered as evidence that the UI is acceptable or not. This distinction between performance and opinion about performance is crucial. Opinions are subjective. Whether a sample of users can accomplish what they want or not is objective. Under many circumstances it is more useful to find out if users can do what they want to do rather than asking someone.
PERFORMING THE TEST
1. Get a person who fits the user profile. Make sure that you are not getting someone who has worked on it.
2. Sit them down in front of a computer, give them the application, and tell them a small scenario, like: “Thank you for volunteering making it easier for users to find what they are looking for. We would like you to answer several questions. There is no right or wrong answers. What we want to learn is why you make the choices you do, what is confusing, why choose one thing and not another, etc. Just talk us through your search and let us know what you are thinking. We have a recorder which is going to capture what you say, so you will have to tell us what you are clicking on as you also tell us what you are thinking. Also think aloud when you are stuck somewhere”
3. Now don’t speak anything. Sounds easy, but see if you actually can shut up.
4. Watch them use the application. If they ask you something, tell them you're not there. Then shut up again.
5. Start noting all the things you will have to change.
6. Afterwards ask them what they thought and note them down.
7. Once the whole thing is done thank the volunteer.
TOOLS AVAILABLE FOR USABILITY TESTING
• ErgoLight Usability Software offers comprehensive GUI quality solutions for the professional Windows application developer. ErgoLight offers solutions for developers of Windows applications for testing and evaluating their usability.
• WebMetrics Tool Suite from National Institute of Standards and Technology contains rapid, remote, and automated tools to help in producing usable web sites. The Web Static Analyzer Tool (WebSAT) checks the html of a web page against numerous usability guidelines. The output from WebSAT consists of identification of potential usability problems, which should be investigated further through user testing. The Web Category Analysis Tool (WebCAT) lets the usability engineer quickly construct and conduct a simple category analysis across the web.
• Bobby from Center for Applied Special Technology is a web-based public service offered by CAST that analyzes web pages for their accessibility to people with disabilities as well as their compatibility with various browsers.
• DRUM from Serco Usability Services is a tool, which has been developed by close cooperation between Human Factors professionals and software engineers to provide a broad range of support for video-assisted observational studies.
• Form Testing Suite from Corporate Research and Advanced Development, Digital Equipment Corporation Provides a test suite developed to test various web browsers. The test results section provides a description of the tests.
USABILITY LABS
• The Usability Center (ULAB) is a full service organization, which provides a "Street-Wise" approach to usability risk management and product usability excellence. It has custom designed ULAB facilities.
• Usability Sciences Corporation has a usability lab in Dallas consisting of two large offices separated by a one way mirror. The test room in each lab is equipped with multiple video cameras, audio equipment, as well as everything a user needs to operate the program. The video control and observation room features five monitors, a video recorder with special effects switching, two-way audio system, remote camera controls, a PC for test log purposes, and a telephone for use as a help desk.
• UserWorks, Inc. (formerly Man-Made Systems) is a consulting firm in the Washington, DC area specializing in the design of user-product interfaces. UserWorks does analyses, market research, user interface design, rapid prototyping, product usability evaluations, competitive testing and analyses, ergonomic analyses, and human factors contract research. UserWorks offers several portable usability labs (audio-video data collection systems) for sale or rent and an observational data logging software product for sale.
• Lodestone Research has usability-testing laboratory with state of the art audio and visual recording and testing equipment. All equipment has been designed to be portable so that it can be taken on the road. The lab consists of a test room and an observation/control room that can seat as many as ten observers. A-V equipment includes two (soon to be 3) fully controllable SVHS cameras, capture/feed capabilities for test participant's PC via scan converter and direct split signal (to VGA "slave" monitors in observation room), up to eight video monitors and four VCA monitors for observer viewing, mixing/editing equipment, and "wiretap" capabilities to monitor and record both sides of telephone conversation (e.g., if participant calls customer support).
• Online Computer Library Center, Inc provides insight into the usability test laboratory. It gives an overview of the infrastructure as well as the process being used in the laboratory.
END GOALS OF USABILITY TESTING
To summarize the goals, it can be said that it makes the software more user friendly. The end result will be:
• Better quality software.
• Software is easier to use.
• Software is more readily accepted by users.
• Shortens the learning curve for new users.
12.3.4 Security Testing
Security testing attempts to verify that protection mechanisms built into a system will, in fact, protect it from improper penetration. During Security testing, password cracking, unauthorized entry into the software, network security are all taken into consideration.
12.3.5 Stress Testing
Stress testing executes a system in a manner that demands resources in abnormal quantity, frequency, or volume. The following types of tests may be conducted during stress testing;
• Special tests may be designed that generate ten interrupts per second, when one or two is the average rate.
• Input data rates may be increases by an order of magnitude to determine how input functions will respond.
• Test Cases that require maximum memory or other resources.
• Test Cases that may cause excessive hunting for disk-resident data.
• Test Cases that my cause thrashing in a virtual operating system.
12.3.6 Performance Testing
Performance testing of a Web site is basically the process of understanding how the Web application and its operating environment respond at various user load levels. In general, we want to measure the Response Time, Throughput, and Utilization of the Web site while simulating attempts by virtual users to simultaneously access the site. One of the main objectives of performance testing is to maintain a Web site with low response time, high throughput, and low utilization.
Response Time
Response Time is the delay experienced when a request is made to the server and the server's response to the client is received. It is usually measured in units of time, such as seconds or milliseconds. Generally speaking, Response Time increases as the inverse of unutilized capacity. It increases slowly at low levels of user load, but increases rapidly as capacity is utilized. Figure 1 demonstrates such typical characteristics of Response Time versus user load.
Figure1. Typical characteristics of latency versus user load
The sudden increase in response time is often caused by the maximum utilization of one or more system resources. For example, most Web servers can be configured to start up a fixed number of threads to handle concurrent user requests. If the number of concurrent requests is greater than the number of threads available, any incoming requests will be placed in a queue and will wait for their turn to be processed. Any time spent in a queue naturally adds extra wait time to the overall Response Time.
To better understand what Response Time means in a typical Web farm, we can divide response time into many segments and categorize these segments into two major types: network response time and application response time. Network response time refers to the time it takes for data to travel from one server to another. Application response time is the time required for data to be processed within a server. Figure 2 shows the different response time in the entire process of a typical Web request.
Figure 2 shows the different response time in the entire process of a typical Web request.
Total Response Time = (N1 + N2 + N3 + N4) + (A1 + A2 + A3)
Where Nx represents the network Response Time and Ax represents the application Response Time.
In general, the Response Time is mainly constrained by N1 and N4. This Response Time represents the method your clients are using to access the Internet. In the most common scenario, e-commerce clients access the Internet using relatively slow dial-up connections. Once Internet access is achieved, a client's request will spend an indeterminate amount of time in the Internet cloud shown in Figure 2 as requests and responses are funneled from router to router across the Internet.
To reduce these networks Response Time (N1 and N4), one common solution is to move the servers and/or Web contents closer to the clients. This can be achieved by hosting your farm of servers or replicating your Web contents with major Internet hosting providers who have redundant high-speed connections to major public and private Internet exchange points, thus reducing the number of network routing hops between the clients and the servers.
Network Response Times N2 and N3 usually depend on the performance of the switching equipment in the server farm. When traffic to the back-end database grows, consider upgrading the switches and network adapters to boost performance.
Reducing application Response Times (A1, A2, and A3) is an art form unto itself because the complexity of server applications can make analyzing performance data and performance tuning quite challenging. Typically, multiple software components interact on the server to service a given request. Response time can be introduced by any of the components. That said, there are ways you can approach the problem:
• First, your application design should minimize round trips wherever possible. Multiple round trips (client to server or application to database) multiply transmission and resource acquisition Response time. Use a single round trip wherever possible.
• You can optimize many server components to improve performance for your configuration. Database tuning is one of the most important areas on which to focus. Optimize stored procedures and indexes.
• Look for contention among threads or components competing for common resources. There are several methods you can use to identify contention bottlenecks. Depending on the specific problem, eliminating a resource contention bottleneck may involve restructuring your code, applying service packs, or upgrading components on your server. Not all resource contention problems can be completely eliminated, but you should strive to reduce them wherever possible. They can become bottlenecks for the entire system.
• Finally, to increase capacity, you may want to upgrade the server hardware (scaling up), if system resources such as CPU or memory are stretched out and have become the bottleneck. Using multiple servers as a cluster (scaling out) may help to lessen the load on an individual server, thus improving system performance and reducing application latencies.
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