@InjectMocks annotation in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the @InjectMocks annotation in JUnit testing?

<p>The <code>@InjectMocks</code> annotation is used to create an instance of the class under test and inject mock dependencies into it automatically.</p>

beginner

How does @InjectMocks differ from @Mock in JUnit tests?

@Mock creates mock objects for dependencies, while @InjectMocks creates the real object and injects those mocks into it.

intermediate

Which injection types does @InjectMocks support for injecting mocks?

@InjectMocks supports constructor injection, setter injection, and field injection to insert mocks into the tested class.

intermediate

What happens if @InjectMocks cannot find a suitable constructor or setter to inject mocks?

<p>The injection will fail silently, and the tested class may have null dependencies, causing NullPointerExceptions during test execution.</p>

beginner

Can @InjectMocks be used without initializing mocks with MockitoAnnotations.openMocks(this) or @ExtendWith(MockitoExtension.class)?

No. To enable @InjectMocks to work, mocks must be initialized either by calling MockitoAnnotations.openMocks(this) in a setup method or using the Mockito extension with JUnit 5.

What does the @InjectMocks annotation do in a JUnit test?

A Runs the test method multiple times

B Creates mock objects for dependencies

C Creates a real instance of the class and injects mocks into it

D Mocks static methods

@InjectMocks creates the real object under test and injects mocks into its dependencies automatically.

Which of the following is NOT a way @InjectMocks injects mocks?

A Constructor injection

B Setter injection

C Field injection

D Interface injection

@InjectMocks supports constructor, setter, and field injection but not interface injection.

What must you do to enable @InjectMocks to work properly in your test class?

A Initialize mocks with <code>MockitoAnnotations.openMocks(this)</code> or use <code>@ExtendWith(MockitoExtension.class)</code>

B Call <code>System.out.println()</code> in the test

C Use <code>@Test</code> annotation only

D Write a main method

Mocks must be initialized for @InjectMocks to inject them properly.

If @InjectMocks cannot find a suitable constructor or setter, what is likely to happen?

A Mocks will be injected anyway

B Dependencies will remain null, causing errors

C Test will pass without any issue

D JUnit will skip the test

Without proper injection points, dependencies remain null, leading to NullPointerExceptions.

Which annotation is used to create mock objects that @InjectMocks will inject?

A @Mock

B @Test

C @BeforeEach

D @Spy

@Mock creates mock objects for dependencies to be injected.

Explain how @InjectMocks works in a JUnit test and why it is useful.

Think about how it helps avoid writing manual code to set dependencies.

Describe the steps needed to properly use @InjectMocks in a test class.

Consider both annotations and mock initialization.