JUnit & Mockito Interview Questions

Resources

  • https://www.tutorialspoint.com/junit/junit_suite_test.htm

  • https://www.tutorialspoint.com/junit/junit_questions_answers.htm

  • https://www.toptal.com/java/unit-integration-junit-tests

  • https://dzone.com/articles/unit-and-integration-tests-in-spring-boot-2

  • Mockito FAQ

Some JUnit questions

  • What is unit testing?
    It is the process of testing individual functionality of an application.
    It is the process of testing individual functionality.

  • How to test a protected method?
    The test class muest be declared in the same package as the target class.

  • How to test a private method?
    There is no way to do it. So you must change the method signature.

  • Can we change the return type of a test method from void to some other?
    No, all junit tests must have a void return type; otherwise, the method is not considered a test.

  • What is is a Test Suit?
    It is used to bundle a few unit test cases and run the together. @RunWith and @Suite.

  • What are the most important JUnit annotations? @Test, @BeforeClass, @Before, @After, @AfterClass, @Ignore.

  • What is a Parameterized test? Allows a developer to run the same test over and over again using different values.

Some Mockito questions

  • What is Mocking and Mockito?
    Mockito is a mocking framework for Java. Mockito allows convenient creation of substitutes of real objects for testing purposes.

  • What is a Mock Object?
    Replaces a mocked class entirely, returning recorded or default values.

  • What is spying? When spying, the real methods are called (unless a method was stubbed). It is suggested to test legacy code.

  • Test Doubles (like stunt double) https://martinfowler.com/bliki/TestDouble.html
    Test Double is a generic term for any case where you replace a production object for testing purposes. There are varios kinds of doubles:

    • Fake: Object replacing the actual code by implementing the same interface but without interacting with other objects. Usually the Fake is hard-coded to return fixed results.
    • Stubs: provides a set of answers to calls, usually not responding at all to anything outside what’s programmed in for the test.
    • Mocks: