Unit Testing Roadmap | Junit with Mockito Basics to Advanced 2025
👉 UNIT TESTING
Available Frameworks:
Junit
TestNG etc.
What is a unit test?
Difference between unit vs integration vs functional tests
AAA (Arrange-Act-Assert)
Maven/Gradle dependencies
Test Lifecycle
Basic Annotations:
• @Test
• @BeforeEach, @AfterEach
• @BeforeAll, @AfterAll
• @DisplayName
• @Disable
etc.
Assertions:
• assertEquals, assertNotEquals
• assertTrue, assertFalse
• assertNull, assertNotNull
• assertThrows for exception testing
Parameterized Tests
Test Repetition
• @RepeatedTest(n)
👉 Mocking
Available Frameworks:
Mockito
EasyMock
JMock
Mockito Core Concepts:
• @Mock and Mockito.mock(Class.class)
• @InjectMocks for injecting mocks
• @BeforeEach with MockitoAnnotations.openMocks(this)
• Testing Private/Static Methods (PowerMock or some other approach)
Stubbing Behavior
• when(...).thenReturn(...)
• when(...).thenThrow(...)
Verifying Calls
• verify(...) after method call
• verifyNoMoreInteractions(...)
Void Method Stubbing
• doNothing().when(mock).method()
• doThrow(...).when(...)
Argument Matchers:
• any(), eq(), anyString(), anyInt(), etc.
• Mixing matchers with exact values (and why it fails)
Behavior Verification:
Verify how many times called: times(n), never(), atLeastOnce()
Spies vs Mocks:
○ Mockito.spy() for partial mocking
○ Difference between mock() and spy()
Testing Configuration, Properties, and Profiles
Unit tests with different Spring profiles.
How to mock @Value, Environment, or @ConfigurationProperties.
Overriding properties for test-only behavior.
👉 Assertions & Matchers
Frameworks:
AssertJ
Hamcrest
👉 Some Advanced Topics
Test-Driven Development (TDD)
Write failing test first, then code
Test Coverage:
• Tools: JaCoCo, IntelliJ coverage tool
CI integration
Run tests in GitHub Actions, GitLab CI/CD, Jenkins.
Test Reports
Generate HTML/XML test reports for build tools.
👉 AI + Unit Testing
Code Suggestion Tools (AI-Powered IDE Extensions)
Using AI in CI/CD (Future-Forward)
AI suggests missing test cases for changed methods
AI flags flaky or redundant tests
Autogenerate Missing Tests
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