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Unit Tests

Unit- and Unit-Integration-Tests Good Practices

This articles focuses on Unit- and Unit-Integration-Tests. General test automation good practices can be found here.

Use TDD to improve code and test quality

Test Driven Development (TDD) is a software development method where tests are written first before the actual code in cycles "make it red, make it green, make it clean". It leads to better tests and often to a better design, because the parts where the logic happens are better structured to allow easy testing. It also leads to better code, because the last step is a refactoring that can be performed safely because of the tests.

Structure your tests with the AAA Pattern

Structure your tests in three sections:

  • Arrange: bring your test object in the desired state.

  • Act: perform one action on your test object and capture the output, if there is any.

  • Assert: verify that your test object has acted in the expected way.

Alternative names are given - when - then.

The sections should be easily distinguishable. This can be done by comments or simply by empty lines (clean code way). Which way is used is a matter of taste but do it in a consistent way.

If there are no initializations, the arrange-section may be empty. The other two sections can never be empty.

A detailed article about the AAA-pattern can be found here.

Use test coverage, but not as a measure for test quality

A high test coverage does not mean you have good tests. But a low test coverage means that much of your code is completely untested. So, this is not an option. That means:

  • Set an adequate objective for code coverage (e.g. 80%); you may exclude packages that do not contain considerable logic.

  • Do not rely on coverage alone, but review tests like other code.

Prefer delegation over inheritance

Unit- and Unit-Integration tests may need cross-cutting functionality. For this, prefer delegation over inheritance to avoid god-super-classes. Good places to put this kind of code can be realized and reused via the JUnit @Rule mechanism.

Technology Stack

  • Junit 5 is the good de-facto standard for Java.

  • Keep the scope of Unit Tests small. This will require mocking of classes that a test object interacts with. Mockito is a good choice for a mocking framework.

  • For mocking remote connections Wiremock is a good choice.

  • Use AssertJ to write good readable assertions that also provide valuable feedback in case a test fails. Do not use legacy JUnit methods like assertEquals anymore.


  • Simple good case

  • Parameterized good cases

  • Parameterized error cases

    void shouldCreateAValidCommonBookingToken() {
        // arrange
        String validCommonToken = "CB_12345";
        // act
        BookingToken token = BookingToken.of(validCommonToken);
        // assert
            "CB_, COMMON",
            "GB_1234 ,INVITED"})
    void shouldCreateValidCommonBookingTokens(String tokenStr, BookingType expectedType) {
        // act
        BookingToken token = BookingToken.of(tokenStr);
        // assert
    @ValueSource(strings = { "A", "CB1233", " ", "122323423423" })
    void shouldDetectInvalidTokens(String token) {
        // act & assert
        assertThrows(WrongTokenException.class, () -> BookingToken.of(token));