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What Is Unit test in Python?



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Unit testing is a technique in which the developer tests a specific module to see if there are any errors. The main goal of unit testing is to test an individual unit of a system to analyze, detect, and correct errors. Python includes the Unit test module for testing source code units. When we are writing large amounts of code, Unit test comes in handy because it allows us to check whether the output is correct or not.

Unit testing is a software testing method that examines the minor testable pieces of code, known as units, and tests them for correct operation. Unit testing allows us to ensure that every part of the code, including helper functions that may not be visible to the user, works correctly and as intended. The idea is that we check each small piece of our program independently to ensure that it works. In contrast, regression and integration testing ensures that the program’s various components work well together and as intended.

Python unit testing should be performed from the beginning and throughout the development process. Unit tests are written to detect bugs early in the application’s development, when bugs are less common and less expensive to fix.

However, if unit tests are poorly designed or run incorrectly, bugs enter the production stage. Therefore, skipping unit testing during the development process will almost certainly cost your company thousands, if not hundreds of thousands, of dollars, depending on the size of the project.

Q1. How does Python Unit Testing work?

When a unit of Python code is finished, the developer is supposed to test it to ensure that:

  • The program has no bugs, and it works correctly for all possible test conditions.

  • It correctly receives input from upstream software units and passes the results to downstream units.

  • Python developers can use manual testing methods to validate their code, but this:

  • It is a time-consuming undertaking.

  • This causes fatigue.

  • Document the test data and results in an unstructured manner.

  • It is not repeatable and can make maintenance work difficult.

  • Hence, Python developers must write scripts for future testing and program maintenance.

Benefits of Python Unit Testing

  1. Unit tests reveal problems early in the development process.
  2. Mitigating change allows the developer to refactor the source code during testing and later, while ensuring the module works as expected.
  3. Integration testing is simplified by first testing the individual components of an application and then testing them all together.
  4. Unit testing with dockets provides a better understanding.
  5. Unit tests can also be run quickly, efficiently, and as frequently as the project demands.
  6. It aids in the detection of bugs early in the development cycle.
  7. It assists you in writing better programs.
  8. It easily integrates with other testing methods and tools.
  9. It is easier to change in the future with minimal impact.
  10. They serve as executable documentation for the application and a valuable reminder of previous bugs you’ve fixed.

Python Unit Testing Methods

Python Unit Testing involves testing a specific module without access to any dependent code. Developers can use techniques such as stubs and mocks to divide code into “units” and test the individual pieces at the unit level.

Development Through Testing


Unit testing should be done alongside Python, and developers should use the Test-Driven Development method.

TDD requires you to first design Python unit tests before writing the code that will implement this feature.

Stubs and mocks

These are two powerful techniques for simulating fake methods that are being tested. A Stub is used to fill in a dependency required for a unit test to run correctly. On the other hand, a mock is a fictitious object that executes the tests where we put assert.

Both methods have the same goal-to eliminating testing all of a class’s or function’s dependencies.


Python includes a package called Unit test that is used to perform unit testing. Unit testing makes the code future-proof because developers anticipate possible failure scenarios and test the code against them. Even if we miss some cases, most of them will be addressed, and the code will be tested against them. Python Unit test is an integrated testing framework for testing Python code. It has a test runner, which allows us to run the tests quickly. Unit tests are small code written by programmers during the development process. It serves as the foundation for component testing. In addition, unit testing is a method of software testing in which individual units of source code, such as functions, procedures, and classes, are tested to see if they are fit for use.

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