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Annotated Mockito Objects Should Be Initialized

High
correctnesstesting

What is it?​

This practice is triggered by test classes containing Mockito annotations @Mock, @Spy, @Captor, or @InjectMocks that are not properly initialized. Uninitialized mocks will cause tests to fail because they are not functional.

Why apply it?​

To ensure Mockito annotations work correctly, they must be explicitly initialized. Failing to do so can lead to inaccurate test results and prevent catching errors effectively.

How to fix it?​

Initialize Mockito objects by using one of the methods provided by the framework:

  • Call MockitoAnnotations.openMocks(this) or MockitoAnnotations.initMocks(this) in a setup method.
  • Annotate the test class with @RunWith(MockitoJUnitRunner.class) for JUnit 4.
  • Annotate the test class with @ExtendWith(MockitoExtension.class) for JUnit 5.
  • Use @Rule public MockitoRule rule = MockitoJUnit.rule(); in the test class.

Examples​

Example 1:​

Negative​

The negative example shows a JUnit 5 test class using Mockito annotations without initialization, which is noncompliant.

import org.junit.jupiter.api.Test;
import org.mockito.Mock;

public class ServiceTest {

  @Mock
  private DataService dataService;

  @Test
  void testDataProcessing() {
    // Test logic here
  }
}

Example 2:​

Positive​

The positive example shows a JUnit 5 test class with Mockito annotations properly initialized using MockitoExtension.

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)
public class ServiceTest {

  @Mock
  private DataService dataService;

  @Test
  void testDataProcessing() {
    // Test logic here
  }
}

Negative​

The negative example displays a JUnit 4 test class without proper initialization of Mockito annotations, leading to noncompliance.

import org.junit.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;

public class CalculatorTest {

  @Mock
  private MathService mathService;

  @InjectMocks
  private Calculator calculator;

  @Test
  public void testAdd() {
    // Test logic here
  }
}

Example 3:​

Positive​

The positive example demonstrates Mockito objects being initialized using MockitoJUnitRunner in a JUnit 4 test class.

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.MockitoJUnitRunner;

@RunWith(MockitoJUnitRunner.class)
public class CalculatorTest {

  @Mock
  private MathService mathService;

  @InjectMocks
  private Calculator calculator;

  @Test
  public void testAdd() {
    // Test logic here
  }
}