Mockito dependency setup in JUnit - Test Execution Trace

Test Overview

This test checks if Mockito is correctly set up in a JUnit 5 project by verifying that a mock object is created and behaves as expected.

Test Code - JUnit 5 with Mockito

JUnit

import static org.mockito.Mockito.*;
import org.junit.jupiter.api.Test;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import org.junit.jupiter.api.extension.ExtendWith;
import static org.junit.jupiter.api.Assertions.*;
import java.util.List;

@ExtendWith(MockitoExtension.class)
public class MockitoSetupTest {

    @Mock
    private List<String> mockedList;

    @Test
    public void testMockCreation() {
        // Arrange
        when(mockedList.size()).thenReturn(3);

        // Act
        int size = mockedList.size();

        // Assert
        assertEquals(3, size, "Mocked list size should be 3");
    }
}

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test starts and JUnit initializes the test class with MockitoExtension	JUnit test runner is ready; MockitoExtension prepares mocks	-	PASS
2	Mockito creates a mock instance of List<String> and injects it into mockedList	mockedList is a Mockito mock object	-	PASS
3	Test sets up behavior: when mockedList.size() is called, return 3	mockedList configured to return 3 for size()	-	PASS
4	Test calls mockedList.size()	mockedList.size() returns 3 as configured	assertEquals(3, size)	PASS
5	Test finishes successfully with assertion passing	Test passed, mock works as expected	assertEquals passed	PASS

Failure Scenario

Failing Condition: MockitoExtension is not registered or Mockito dependency is missing, so mock is not created

Execution Trace Quiz - 3 Questions

What does the @ExtendWith(MockitoExtension.class) annotation do in this test?

A It disables Mockito for this test

B It runs the test in a separate thread

C It initializes Mockito mocks before each test

D It sets the test timeout

Key Result

Always use @ExtendWith(MockitoExtension.class) in JUnit 5 tests to enable Mockito annotations and ensure mocks are properly created before tests run.