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What is unit testing? How can it be carried out?

What is unit testing? How can it be carried out?

Unit testing is a way to verify that a code snippet works correctly. It’s one of the procedures implemented within an agile work methodology. 

If you have never dared to carry it out or don’t know where to start, this article is intended for you. Find out how unit testing can help you improve your application’s end result.

Index – What unit testing is and how to carry it out


What is unit testing?

Unit testing consists of isolating a part of the code and verifying that it works perfectly. It involves small tests that validate the behaviour of an object and the logic behind the code.

Unit testing is usually carried out during the development stage of mobile or software applications. These tests are normally carried out by developers although, for all practical purposes, they can also be carried out by QA assurance managers.

There is somewhat of a mystery shrouding unit testing. Some developers are convinced that these tests are a waste of time and avoid them altogether believing they’ll be saving time.

There’s nothing further from reality.

By carrying them out, errors can be detected much earlier − errors which, without unit testing, would not be detected until more advanced stages such as system, integration or even beta testing.

Performing unit testing regularly ultimately means saving time and money.


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Reasons for carrying out unit testing

If you are still not sure why you should incorporate unit testing into your everyday life as a developer, here are some reasons to do so:

  • Unit testing reveals if the logic behind the code is appropriate and will work in all cases.
  • It boosts the code’s readability and helps developers understand the base code, making it easier to implement changes faster.
  • Well-conducted unit testing is also good as project documentation.
  • The tests are carried out in just over a few milliseconds, so you can perform hundreds of them within a very short time.


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  • Unit testing allows the developer to refactor the code later on and ensure that the module keeps on working properly. Test cases are written to this effect for all functions and methods so that errors may be quickly identified and repaired every time any of them is created by the introduction of a change in the code.
  • The code’s final quality will improve because it will ultimately be a clean high-quality code due to this continuous testing.
  • Since unit testing divides the code into small snippets or fragments, it’s possible to test different parts of the project without having to wait for other parts to be completed.


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The 3 A’s of unit testing

To perform fitting unit tests, these must be structured following the three A’s of unit testing. The three A’s of unit testing make up a fundamental concept regarding this kind of tests, describing a three-step process.

  • Arrange. It’s the first step in unit testing. This step defines the requirements that must be met by the code.
  • Act. It’s the intermediate step of the tests: the moment when the test is run, yielding the results that you will subsequently have to analyse.
  • Assert. In this last step, the results will have to be checked to see if they are as expected. If this is the case, it gets validated and you can carry on. If not, any possible errors will have to be corrected until they stop showing up.




How to implement the 3 A’s

The unit testing process can be carried out manually, although it’s more common to automate the procedure by means of certain tools.

There are many options available, which vary depending on the programming language being used. The following are some examples of this kind of tools, which will help you out with the testing.

  • xUnit: it’s a unit testing tool to be used on the .NET framework.
  • JUnit: it’s a set of libraries for unit testing on Java applications.
  • NUnit: NUnit 3 − which was initially ported from JUnit − has been completely rewritten to provide it with new features and support for a wide range of .NET platforms.
  • PHPUnit: it’s a unit testing environment for the PHP programming language.

When using these tools, the criteria that will verify whether the code is correct or not are coded in the test. Then, during the execution stage, the tool will detect which tests have revealed the presence of errors in the code.

If any of these errors are serious, you may stop any subsequent tests that were to be performed.


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TDD and unit testing

Test-driven development (TDD) involves developing the unit testing procedures to be performed on the piece of software before writing the software’s code.

Development is, thus, carried out according to the requirements that have been established in the test that must be passed by the code. The goal is to get a clean code that works.

When following this methodology, a requirement is chosen from a list of requirements and a test is set out and performed to check what might be going wrong. If there’s nothing going wrong, it may be either because the test wasn’t set out correctly to begin with or because the function to meet the requirement is already well implemented.

The code that enables passing the test by the simplest possible means is then written down. The tests are then performed again and, if everything goes right, the code is ultimately refactored in order to eliminate duplicate parts.

This way you’ll be able to tick that particular requirement off from the list and move ahead with the development process.

Good practices for unit testing

You will discover all the advantages of unit testing once you get used to performing this kind of tests. However, let’s have a look at some examples of good practices for software unit testing just in case you are still not fully acquainted with the matter.

  • Unit tests should be independent. Unit tests should remain unaffected should any kind of improvement or change in the requirements occur.
  • Test only one code snippet at a time.
  • Follow a clear outline. This may seem incidental to other practices, but it is not. Be consistent when naming your unit tests.
  • Any change implemented needs to pass the tests. If there’s a change in the code of any of the modules, make sure that there are unit tests relevant to such a module and that such a module passes the tests before fully implementing the change.
  • Fix any bugs that may have been identified during the tests before carrying on. Make sure to get this right before carrying on to the next stage of the software development life cycle.
  • Get used to performing tests regularly while programming. The more code you write without testing, the more paths you will have to check for possible errors.

You can’t expect unit testing to reveal all the errors that a piece of software might contain, but it does save you a lot of time by making it easier to pinpoint errors.

As you can see, there are multiple advantages to be obtained from incorporating unit testing into your everyday development work. Are you ready?

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