Software Testability

Software testing is a vital activity to be performed during software development to release bug-free software that meets customer requirements. Testability is the ease with which a system can be tested. It enables easy assessment and determining the overall efforts required for performing the testing activities on the software. The article focuses on discussing the following topics of Software Testability:

1. What is Software Testability?
2. Factors of Software Testability
3. How to Measure Software Testability?
4. Requirements of Software Testability
5. Types of Software Testability
6. Improving Software Testability
7. Benefits of Software Testability

Let’s start discussing each of these topics in detail.

What is Software Testability?

Software testability is measured with respect to the efficiency and effectiveness of testing. Efficient software architecture is very important for software testability. Software testing is a time-consuming, necessary activity in the software development lifecycle, and making this activity easier is one of the important tasks for software companies as it helps to reduce costs and increase the probability of finding bugs. There are certain metrics that could be used to measure testability in most of its aspects. Sometimes, testability is used to mean how adequately a particular set of tests will cover the product.

• Testability helps to determine the efforts required to execute test activities.
• Less the testability larger will be efforts required for testing and vice versa.

Factors of Software Testability

Below are some of the metrics to measure software testability:

1. Operability: “The better it works, the more efficiently it can be tested.” 

• The system has a few bugs (bugs add analysis and reporting overhead to the test process).
• No bugs block the execution of tests. 
• The product evolves in functional stages (allows simultaneous development testing).

2. Observability: “What you see is what you test.”

• Distinct output is generated for each input.
  System states and variables are visible or queriable during execution. Past system states and variables are visible or queriable. For example, transaction logs.
• All factors affecting the output are visible.
• Incorrect output is easily identified.
• Internal errors are automatically detected through self-testing mechanisms. o Internal errors are automatically reported. co Source code is accessible.

3. Controllability: “The better we can control the software, the more the testing can be automated and optimized.”

• All possible outputs can be generated through some combination of inputs. All code is executable through some combination of input.
• Software and hardware states and variables can be controlled directly by the test engineer.
• Input and output formats are consistent and structured. 

4. Decomposability: “By controlling the scope of testing, we can more problems and perform smarter retesting.” quickly isolate

• The software system is built from independent modules.
• Software modules can be tested independently. 

5. Simplicity: “The less there is to test, the more quickly we can test it.”

• Functional simplicity (e.g., the feature set is the minimum necessary to meet requirements).
• Structural simplicity (e.g., architecture is modularized to limit the propagation of faults).
• Code simplicity (e.g., a coding standard is adopted for ease of inspection and maintenance).

6. Stability: “The fewer the changes, the fewer the disruptions to testing.” Changes to the software are infrequent.

• Changes to the software are controlled.
• Changes to the software do not invalidate existing tests. The software recovers well from failures.

7. Understandability: “The more information we have, the smarter we will test.”

• The design is well understood.
• Dependencies between internal, external, and shared components are well
• understood.
• Changes to the design are communicated. Technical documentation is instantly accessible.
• Technical documentation is well organized. Technical documentation is specific and detailed.
• Technical documentation is accurate.

8. Availability: “The more accessible objects are the easier is to design test cases”. It is all about the accessibility of objects or entities for performing the testing, including bugs, source code, etc.

9. Testing Tools: Testing tools that are easy to use will reduce the staff size and less training will be required.

10. Documentation: Specifications and requirements documents should be according to the client’s needs and fully featured.

How to Measure Software Testability?

Software testability evaluates how easy it is to test the software and how likely software testing will find the defects in the application. Software testability assessment can be accomplished through software metrics assessment:

• Depth of Inheritance Tree.
• Fan Out (FOUT).
• Lack Of Cohesion Of Methods (LCOM).
• Lines Of Code per Class (LOCC).
• Response For Class (RFC).
• Weighted Methods per Class (WMC).

During software launch, it is crucial to determine which components may be more challenging to test. Software testability assessment is crucial during the start of the testing phase as it affects the efficiency of the planning process. 

Requirements of Software Testability

The attributes suggested by Bach can be used by a software engineer to develop a software configuration (i.e., programs, data, and documents) that is amenable to testing. Below are some of the capabilities that are associated with software testability requirements:

• Module capabilities: Software is developed in modules and each module will be tested separately. Test cases will be designed for each module and then the interaction between the modules will be tested.
• Testing support capabilities: The entry point to test drivers and root must be saved for each person, test interface as during the increment level testing, the trouble and accuracy level of testing root and driver should be given high priority and importance.
• Defects disclosure capabilities: The system errors should be less so that they do not block the software testing. The requirement document should also pass the following parameters to be testable:
  • The requirement must be accurate, correct, concise, and complete. 
  • The requirement should be unambiguous i.e it should have one meaning for all staff members.
  • A requirement should not contradict other requirements.
  • Priority-based ranking of requirements should be implemented.
  • A requirement must be domain-based so that the changing requirements won’t be a challenge to implement.
• Observation capabilities: Observing the software to monitor the inputs, their outcomes, and the factors influencing them.

Types of Software Testability

Below are the different types of software testability:

1. Object-oriented programs testability: Software testing object-oriented software is done at three levels, Unit, Integration, and System testing. Unit testing is the most accessible level to get better software testability as one can apply testability examination earlier in the improvement life-cycle.

2. Domain-based testability: Software products that are developed with the concept of domain-driven development are easy to test and changes can be also done easily. The domain testable software is modifiable to make it observable and controllable.

3. Testability based on modules: The module-based approach for software testability consists of three stages:

• Normalize program: In this stage, the program needs to be normalized using some semantic and systematic tools to make it more reasonable for testability measures.
• Recognize testable components: In this stage, the testable components are recognized based on the demonstrated normalized data flow.
• Measure program testability: Program testability is measured based on the information stream testing criteria.

Improving Software Testability

Below are some of the parameters that can be implemented in practice to improve software testability:

•  Appropriate test environment: If the test environment corresponds to the production environment then testing will be more accurate and easier.
• Adding tools for testers: Building special instruments for manual testing helps to make the process easier and simpler.
• Consistent element naming: If the developers can ensure that they are naming the elements correctly, consistently, logically, and uniquely then it makes testing more convenient. Although this approach is difficult in larger projects with multiple developers and engineers.
• Improve observability: Improving observability provides unique outputs for unique inputs for the Software Under Test.
• Adding assertions: Adding assertions to the units in the software code helps to make the software more testable and find more defects.
• Manipulating coupling: Manipulating coupling to make it Domain dependent relative to the increased testability of code.
• Internal logging: If software accurately logs the internal state then manual testing can be streamlined and it enables to check of what is happening during any test.
• Consistent UI design: Consistent UI design also helps to improve software testability as the testers can easily comprehend how the user interface principles work.

Benefits of software testability

• Minimizes testers’ efforts: Testability calculates and minimizes the testers’ efforts to perform testing as improved software testability facilitates estimating the difficulty in finding the software flaws.
• Determines the volume of automated testing: Software testability determines the volume of automated testing based on the software product’s controllability.
• Early detection of bugs: Software testability helps in the early and effortless detection of bugs and thus saves time, cost, and effort required in the software development process.