Software Unit Testing: What is That? Why is it Important?

Anna Khrupa

3 m read


Testing & QA, Unit Testing

Software unit testing: What is it? Why is it important?

It is hard to overestimate the importance of software quality. A single error can have a huge negative impact on your entire business. If bug issues are not addressed efficiently, it may result in everything from an endless cycle of fixes to a completely destroyed reputation of your company. Effective testing strategies help to minimize such risks by ensuring the quality of the released product. There are many testing practices you can choose to build a great software solution. One of the basic but effective testing techniques to make sure that your product works properly is called unit testing.

What is unit testing and what are the unit testing frameworks?

Unit testing (sometimes called module testing or component testing) is a technique for testing the smallest testable component of your code (unit) to ensure that it performs as intended. The basic feature of unit testing is the isolation – a unit test only performs a specific function and excludes all external influences, such as dependencies between units, calls to other functions, etc The unit testing process can be done manually, but developers usually use unit testing tools to facilitate the process, so they can focus on more complex tasks such as defining the test cases.

For almost all programming languages there is a suitable unit test software that reads the source text and reviews it for errors. For example, there are JUnit for the Java programming language, CUnit for the C programming language, or JSUnit for the JavaScript programming language. In some languages, the test framework is already an integral part of its standard library. For example, Python’s library includes a module called unittest which is used to test the components of the code.

The benefits of unit testing in software development

Unit testing brings a lot of benefits to the development process. This technique allows examining the components of the software separately to make sure that each performs as expected. With the help of unit testing, you can localize every little mistake quickly and accurately as well as simplify the debugging process if any issue occurs. Moreover, unit tests give the ability to detect errors at an early stage of the development process before it reaches QA or end-users. It should be also noted that this technique helps to save time and costs in terms of future developments.

The main idea of unit tests lies in improving the quality of the software. In particular, unit testing ensures that not exposed or hardly accessible functionality of the product works as designed. What is important that unit testing also serves as credible proof for the quality of the technology your product is built with. By using unit testing best practices, you can also check the stability of the software, for example, how it reacts to malicious use.

Unit tests serve as the alignment between specification and the result of development. By running unit tests, it is easy to check if the program component delivers what was specified in the requirements. And finally, if you make changes to software, unit tests may be a cheap way to make sure that the system still works fine and none of the functionalities is broken.

What is the difference between unit testing and test drive development?

Unit testing is a technique that allows testing the smallest parts of the code individually and independently. Unit tests can be written before or after the code is implemented. Unlike unit testing, test-driven development is not a practice but a design method that uses tests to define the functions of the code to be written.

The development process within TDD takes place according to previously defined requirements. While applying the TDD methodology, a prerequisite is selected from a list of requirements and a test is created and run to check what might go wrong (it’s called the red phase). If nothing goes wrong, it can either be because the test was not properly written or because the function is already well implemented. In the next phase (the green phase) you write the code to make the test pass. And the last phase of the TDD cycle is aimed at refactoring both the code and the test in order to make the code more efficient. So, the main objective of test-driven development is to improve the code during the development process and thus to create a bug-free code that works.

The tests generated during the test-driven development can be unit tests, functional tests, and acceptance tests. Yet when we speak about the tests used in TDD we usually mean unit tests, the difference is that in TDD they are always created before the code is written. It is worth mentioning that the application of unit tests is not equated with the test-driven development as unit tests can be implemented later.

It’s a long way from test planning to unit testing. But we’ll get you there quickly!


Unit testing is a powerful tool that brings a lot of benefits to software development. On one hand, you have a chance to catch and fix the bugs earlier, and on the other hand, you can improve the quality of the software significantly. Unit tests have proved themselves to be a great technique within developing testing and TDD processes that help not only to refine the code but also to save money.

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