Testing in Java

You already recognize the importance of testing your code. Automated testing in Java, like any language, ensures that your code works as expected, every time it runs. Tests also function as documentation, giving an observer instructions on how to properly execute your classes and methods.

This course covers unit testing in Java with a test runner called JUnit. Unit testing breaks down the codebase into its smallest building blocks, which are individual statements and methods.


If you’re not yet familiar with the benefits of automated testing, you can familiarize yourself here .

Why We Test


Because they work on the most basic functionality of your code, unit tests safeguard against bugs introduced in refactoring. Refactoring refers to the process of rewriting code without adding new features.

Imagine this common workflow:

  1. You practice TDD, writing your tests to stipulate your class’s code.

  2. You write your code to pass your tests.

  3. Later, a stakeholder in your project’s use requests that you refactor your code using different syntax.

The features will be the same, but the implementation changes. Unit tests help in this scenario in that changes to implementation should not require changes to outcome. Thus, if your tests continue to pass after the refactor, you can move on, knowing you have not inadvertently introduced a bug. When you write tests once, they provide a code lifetime’s worth of benefits.


Unit tests are the most enlightened form of documentation. Again, because they address the most fundamental tasks of your classes, unit tests serve as live-code use-cases. You may also have an external documentation directory with examples of how to run your project, or perhaps you have been writing comments within your code to best communicate with your teammates about your changes. Both of these are great choices and should be done when possible. However, they also require more forethought to maintain. Each time you update your code, you might not remember to update the documentation and comments. With unit testing, however, you have a more obvious reminder that a change has been made if a test fails.

Testing Best Practices

Below are some best practices to keep in mind when writing unit tests, in any language.

  1. The AAAs

    The AAAs of unit testing refers to the pattern to follow when writing your unit tests.

    1. Arrange the variables your test requires
    2. Act on the methods your test requires
    3. Assert the anticipated comparison of the expected and actual values
  2. Deterministic

    Every, single, solitary time a test is run, it should produce the same outcome. A test that passes only most of the time is a worthless test.

  3. Relevant

    Tests, as they are written, should be grouped by related class and function.

  4. Meaningful

    There is no need to test trivial code. For example, unless they contain additional functionality, there is no need to write tests for getters and setters. Your IntelliJ IDE offers code completion for these anyway.

Check Your Understanding


True or False: Comments are the best tool to make your code readable.


Unit tests are a form of:

  1. Manual testing
  2. Automated testing
  3. Integration testing
  4. Documentation testing