Software Testability: What it is, Types & How to Measure It

May 28, 2024Shreya Bose
Software Testability What it is, Types & How to Measure It

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All software must be tested before it becomes publicly available. This is common knowledge. 

However, software doesn’t just need to be easy to use. It also needs to be easy to test. When developing the blueprint of a software’s hardware and software configuration, one of the many factors (usability, reliability, audience appeal, etc) that needs to be considered is “Can it be easily tested?”

In other words, there should be a significant focus on software testability. In this article, we’ll be introducing you to the fundamental concepts of software testability: what it means, why it matters, types, requirements, metrics, and benefits of improving software testability. 

What is Testability?

Testability is a metric that defines how easily, effectively, and efficiently an application can be tested by QA teams. 

This may sound a little vague. Isn’t all software technically “easy to test”? You just use it to initiate the functions already built into it and check if it performs them all accurately. 

However, testing efficacy is heavily dependent on the software’s underlying architecture. QA professionals need complete knowledge of the application-under-test in order to design and execute requisite tests. They have to understand the behavior and features the app is expected to display and accomplish at all times so that they know what counts as “passing” or “failing” a test. 

This is easier said than done when it comes to complex systems. It takes more time and effort to understand the technical schema, deciding upon the right tests, design said tests, run them, and identify bugs, and run debugging activities. The more complex a system, the less its testability. 

Basically, testability is a measure of how easy or difficult it is to confirm the success/failure of every software module, subsystem, component, and requirement in the application ecosystem. 

Of course, certain software systems (such as, for eg., the computers used to map the skies in astrophysics labs) will have to be more complex if they are to work. But, as far as possible, it is advisable to design source code for high testability. 

Why does Software Testability Matter?

Let’s take an example. 

In a certain project, devs are looking for the root cause of a certain bug by looking through test logs. However, while there are detailed logs for certain modules, others do not. This is because different testers are working on different modules – one maintains logs for everything and the other only logs in the event of a serious malfunction. 

But, when put together, the devs can’t distinguish between the detailed and non-detailed logs, so it’s harder to find the source of the bug. This is the definition of a software product with low testability. 

The solution is to have precise, consistent blogs for all modules, whether or not they trigger bugs. This consistency is what will make the software easier to test, and therefore, more testable. 

The more testable a software, the more successfully testers will be able to scan through and identify the maximum number of bugs. Tests are easier to create and execute. Bugs are found faster and are also easier to resolve. Testers don’t have to spend as much time and effort, and the product hits the market much faster. 

On the other hand, if testability is low, tests are harder to design and take longer to execute. If faced with a tight deadline, the manager might have to sacrifice some tests and push through a buggy product. 

This is why ‘software testability’ or ‘testability in software testing’ matters. 

Factors of Testability in Software

Observability: The ability to detect each software module and components’ response to user inputs. It also involves monitoring the changes the inputs implement in the system’s internal processes. Testable software makes this process as simple as possible, since observing these responses is the basis of tests. Read here – Test Observability.

Controllability: The ability to control every single software module in isolation. The more controllable an app, the more testable it is. Controlling every module makes it easier to automate tests pertaining to each specific module. 

Simplicity: The measure of how much effort devs and QAs need to test an app. This is decided after evaluating the functional, structural, and code-level simplicity. The higher your software simplicity, the more testable (and debugable) it is. 

Stability: The measure of how many or few changes a certain app will require, once it has been put through the relevant tests. A high-stability software will require far fewer changes than it’s low-stability counterpart. Software stability is also required before QAs can start running automated tests. Needless to say, the high the software stability, the more testable it is. 

Know more about automated web application testing here:

Availability: The measure of how available all objects and entities needed for testing (bugs, source code, software components) are at any stage of development. High testability is a direct result of high availability. 

Requirements of Software Testability

Use the attributes mentioned & described below to create a more testable software system. By incorporating these requirements into the configuration(documents, programs, data points), you stand a higher chance of ensuring high testability. Basically, do the following and your software will be easier to test. 

Module capabilities

Each software module is, in the ideal, best-practice-driven scenarios, tested separately. Test cases should be designed for each module, and also designed to gauge the quality and consequence of interaction between the modules. 

Module capabilities include checking for the following:

  • Can each module be tested in isolation?
  • Can each module be tested with every other relevant module?
  • Can every module be tested (if needed) with third-party hardware and software modules?
  • Can every module be tested with its own data?

If the answer to the above questions is yes, you have high-testability software on your hands. 

Test support capabilities

During active tests, the entry point to test drivers and root must be saved for every tester working on the system, every test interface, and test scenario. This is so that, during increment-level testing, you don’t have trouble gauging the accuracy of the testing root and driver. 

Defect disclosure capabilities

System errors should be minimal so that they do not show up as blockers to larger testing. Testers must be aware of all defects that can cause system anomalies (for eg., certain defects lead to performance problems while other causes security vulnerabilities and can lead to DoS attacks). Understanding and disclosing as many defects as possible is the very cornerstone of high software testability. 

Requirement documents must also insist upon the following parameters for high testability:

  • Every single requirement should be precise, brief, and complete. 
  • Each requirement should be unambiguous – it’s meaning should be the same for every dev and tester who sees it. 
  • Every requirement should be in no contradiction with any other requirement. 
  • Every requirement should be ranked on the basis of priority. 
  • Every requirement should be domain-based. This minimized problems if requirements do need to be changed, whether during ideation, software development, and/or testing. 

Observation capabilities

The software should have some mechanisms (or the team should use the right tools) to monitor user inputs, output and factors influencing said output. Examples of such capabilities would be static analysis, dynamic analysis, and functional analysis. 

Types of Testability in Software

Object-oriented program testability

Object-oriented software is tested at the levels of Unit, Integration, and System verification. Of all three, it is easiest to access unit tests to improve testability. This is because unit tests are the very beginning of any test cycle, and any changes for more testability, implemented at this level, will positively affect the entire cycle down the line. 

Domain-based testability

Any software created with the mechanics of domain-driven development will be easy to test and change. The key to making domain-based software more testable is to establish high levels of observability and controllability. 

Module-based testability

To make module-based software highly testable, devs need to account for three stages:

  • Normalize program: Normalize the program via semantic & system tools so that it is more equipped to absorb and work with initiatives driving high testability.
  • Identify testability components: Detect the testable components based on your normalized data pathways and workflows.
  • Measure program testability: Evaluate and gauge program testability on the basis of the testing criteria required by the aforementioned data stream. 

How to Measure Software Testability?

Fundamentally, measuring software testability means finding and specifying the software components that are of questionable quality (at this stage), and distinguishing them from components that have less apparent defects. Low-quality components will be harder to test, so they should be prioritized beneath the low-defect, easier-to-test components. 

However, to determine which component holds what testability, your team needs to look closely at the following metrics:

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)

All these metrics determine, at the core, which components are more challenging to test, and vice-versa. This is something testers need to know at the very beginning of testing, even before they start creating scripts so that they can plan test scenarios, test cases and request equipment (specific test environments) more efficiently.  

The metrics assess how testable the application is and will be through it’s entire lifecycle. Each metric is related to one or more of the testability factors detailed previously in this article. 

Benefits of Software Testability

  • Facilitates earlier detection of bugs/anomalies: Since high testability enables more voluminous and comprehensive testing right from the beginning, QAs end up identifying more bugs at the early stages of a test cycle.

    This is great because bugs detected earlier are easier to remove. They are not as inextricably entwined into the larger system as they would be, if they were later in the cycle.
  • Makes life easier for testers: This is a no-brainer, right? High testability makes software easier to test, which means testers do not have to spend as much time & work to create the right tests, find bugs and report them to devs.
  • Makes it easier to evaluate automation needs: Software testability levels depend heavily on controllability. The level of controllability inherent in a software system is directly related to how much automation it can take. In other words, software testability helps evaluate the level of test automation required for a certain project. 

Improving Software Testability

  • Name elements correctly & obviously: When devs label each element in line with logic and uniqueness, it is much easier, from an admin point of view, to run tests. However, this isn’t always possible, especially in large-scale projects.

    When multiple teams of devs, engineers and testers are working on a single project, they aren’t always aware of the naming convention used by other teams. Im such cases, unique naming is often a casualty.
  • Testing in the appropriate environment: Testing is infinitely easier if the test environments mimic the production environment as closely as possible. It is advisable to run tests on real browsers, devices, and OSes that your target audience is most likely to use.

    Testsigma is a unified, fully customizable software testing platform that works out of the box. It is designed to help automate and execute end-to-end tests 5X faster for web, mobile apps, & APIs. You can use Testsigma to create test scripts in plain English scripts – scripts that self-heal and require low or no maintenance.

You can run tests in your local browser/device or run across 800+ browsers and 2000+ devices on our cloud-hosted test lab. You can also view step-wise results for each test and analyze real-time reports & dashboards at the individual, test suite & device levels. Moreover, Testsigma’s intelligent AI automatically fixes broken scripts, heals dynamically changing elements, and suggests fixes for test failures.

  • Logging mechanisms: Tests are most effectively streamlined if the test software automatically logs the state of the application before and after every test. The logs should also track every single test step, so that devs can go back and check at which step a bug occurred. This makes it easier to identify the cause of the bug.
  • A stable, consistent UI design: Consistent design makes it easy to predict how software components & modules will behave, which in turn, makes it easiest to create tests that provide sufficient test & code coverage.
  • Better observability: Once again, you need a tool like Testsigma to achieve this. Improved observability lets testers look closely at the software output in response to every single input.

Automate your tests for web, mobile, desktop applications and APIs, 5x faster, with TestsigmaAutomate your tests for web, mobile, desktop applications and APIs, 5x faster, with Testsigma


Software testability is the key to creating software that isn’t just highly functional but also allows for seamless testing of those functionalities. No matter how sophisticated your software, if it cannot be tested, it cannot be released. If it is released without testing, bugs will show up for your users….and that is the worst outcome for any software release, ever. 

Frequently Asked Questions

What is an example of testability?

A common example of testability can be found in controllability. If testers can control every (or the majority of) software component with relative ease, then it will be easier to create and run tests on each module. Higher controllability leads to better chances of isolating the components and monitoring it’s responses to each test. 

In other words, software with high controllability has high testability. This is what testability looks like.

What is the difference between testing and testability?

“Testing” refers to the act of actually putting software through a set of tests meant to verify software quality and functionality. “Testability” is a measure of how easy/difficult it is to build and run those tests in reality.

Phases of testing
6 Key Phases of Testing in Software Testing
Test Efficiency
Test Efficiency: How It Differs From Test Effectiveness?
Principles of Software Testing
7 Principles of Software Testing to Ace your Testing Process
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