Unit Tests vs Regression Tests – How to Spot the Difference

Testers are always on the lookout for bugs.

It’s their job to spot errors, risks, and potential safety hazards in software before they have time to cause any harm.

Unit tests are tests that ensure the individual units of code work as they should do. Developers can write these tests. Regression tests focus on older parts of the system and ensure they still work after developers made changes in newer parts. They can be any other kind of automated or manual tests.

Regression testing is a type of software testing which is often confused with unit testing. This blog post will teach you how to spot the difference between these two types of tests and why it’s essential to know the difference to get the most out of your testing efforts.

Unit tests

Unit tests are performed on the smallest unit of code, usually the method, to test the logic of the software. They are typically limited to a few behaviors and components and require no knowledge of the entire system. Instead, developers write them to verify behaviors within the individual units.

unit testing

Software developers can write unit tests before or after writing the production code to ensure the software meets the requirements. When a developer writes a test case before the actual implementation, that is called test-driven development.

If you don’t write unit tests, then you have to check that the application works manually. But when you are focused on writing the functionality, you are less likely to thoroughly and manually check that everything works correctly. Every automated test means you have to spend less time doing manual testing.

A unit test is just one of many possible types of tests that can be executed on any program, application, or software to determine if it meets its design goals. Unit tests are small, independent pieces of code, and are usually part of the application’s solution.

Unit tests are a critical part of the development process because they help programmers ensure that software meets expectations and works.

Regression tests

Software bugs are a common occurrence in the process of software development. They can be caused by human error or an incomplete understanding of the code.

Regression testing is when you update or change your code and then test to ensure nothing else has broken. If there are issues, this is software regression, and you need to fix the bugs before release. This type of testing is essential because it ensures that your product is up-to-date and fully functional.

Regression tests can include:

  • unit testing
  • integration testing
  • UI testing
  • manual testing
  • accessibility testing
  • security testing
  • performance testing
  • exploratory testing

All unit tests are regression tests, but not all regression tests are unit tests.

The regression testing process usually focuses on old or existing newer parts of the system and ensures they still work after the latest changes. So, if you run a regression test on a feature you’ve just deployed, you usually do that on a test server. You can deploy that code to the production only when there are no regression bugs in the testing environment.

Regression tests are a safety net in software development that allows the system to be tested periodically to keep it stable.

You want to avoid a “hydra effect” in your application: where you eliminate one bug in one area but introduce two new bugs in other areas of the application.

Unit tests vs regression tests – the differences

You can use unit and regression tests to check that software and its features work and behave as expected. But there are differences in test goals, test phase, and the amount of code they cover.

The difference in test goals

Unit testing and regression tests are much alike, but they target different areas of your code. Programmers do unit testing, and it checks the function of the individual components of your code. It ensures that each variable, function, and object is working as expected.

Testers do regression testing (also known as QA testing) after programmers finish the work on specific features. Manual regression testing works as a system-wide check to ensure that components that programmers didn’t touch still work as expected. Unit tests ensure that individual functions and variables are working as intended and regression tests work together to ensure that all parts of a system work as intended.

The difference in phase of the development process

The other difference between unit and regression tests is in the stage when they are performed. Unit tests are executed during the development phase, where developers run them after making the changes to ensure they haven’t broken anything.

On the other hand, the team performs regression testing before the feature is released to production. It might include unit tests, integration tests, and any different types of testing. The testers are responsible for performing the regression testing.

Usually, you set up a continuous integration/continuous delivery server, and one of the first steps is to run the unit and integration test suite automatically. This is automated regression testing. If they fail, this means the latest code change has broken the existing code, and the developer needs to check what’s wrong. On the other hand, if the automated testing passes, then testers can manually perform the functional testing of the system.

The difference in the amount of code they cover

The unit test covers one unit, one method, or function. It focuses on one thing at a time and doesn’t take into account how units work combined. To do that, you need an integration test. A unit test provides fast feedback because there’s only one thing being tested at a time.

On the other hand, regression tests check if changes to existing functionality have broken anything else across the whole system by testing against known scenarios. They check if the units have been integrated correctly. Since it involves a lot more testing, it usually takes a bit more time.


There is a big difference between regression and unit tests: the two tests do not belong to the same phase of the testing process, but they are equally important for software development.

Unit tests are the protection against defects in the development phase. You can execute them quickly and often to get feedback about your changes in one area of the code.

Regression tests, on the other hand, are designed to protect existing software functionality against bugs that might be introduced by changes made to the system.

Use both unit and regression tests to minimize the number of bugs end-users see in production.

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