Testing, Debugging & Code Quality

What you will be able to do

• Write clear unit tests with JUnit 5 and AssertJ for real classes
• Isolate code under test with Mockito mocks and stubs
• Test Spring controllers, repositories and whole application flows
• Find bugs quickly with the IDE debugger and useful logs
• Measure test coverage and keep code clean with refactoring and static analysis
• Add a dependable test suite to ShopLite

What it will cover

1. 18.1Why Testing Matters

   What tests protect you from and which kinds of tests to write.

   Show 5 topics
   • Manual testing vs automated testing
   • Unit, integration and end-to-end tests
   • The test pyramid
   • What makes a test good: fast, isolated, readable
   • Tests in the Maven build

2. 18.2JUnit 5 in Depth

   Go past simple assertions to well-organised, data-driven tests.

   Show 6 topics
   • Test structure: Arrange, Act, Assert
   • Lifecycle: @BeforeEach, @AfterEach, @BeforeAll
   • Testing exceptions and timeouts
   • Parameterised tests with @ValueSource and @CsvSource
   • Readable assertions with AssertJ
   • Naming and organising tests

3. 18.3Test-Driven Development

   Write the test first and let it shape the design.

   Show 4 topics
   • Red, green, refactor
   • TDD kata: a discount calculator
   • Testing edge cases and boundaries
   • When TDD helps and when it does not

4. 18.4Mocking with Mockito

   Test one class at a time by replacing its dependencies with mocks.

   Show 6 topics
   • Why mock: slow, external or unfinished dependencies
   • @Mock, @InjectMocks and when/thenReturn
   • verify and argument captors
   • Stubbing exceptions
   • Mocks vs stubs vs fakes
   • Over-mocking and brittle tests

5. 18.5Testing Spring Applications

   Test each layer of a Spring Boot app with the right test slice.

   Show 6 topics
   • Unit testing services without Spring
   • @WebMvcTest and MockMvc for controllers
   • @DataJpaTest for repositories
   • @SpringBootTest for full flows
   • Testing secured endpoints with mock users
   • Test data and test profiles

6. 18.6Debugging

   Find the cause of a bug with the debugger instead of guessing.

   Show 6 topics
   • Breakpoints, step over, step into
   • Watching variables and evaluating expressions
   • Conditional breakpoints
   • Reading stack traces from top to bottom
   • Debugging a running Spring Boot app
   • A step-by-step bug hunting routine

7. 18.7Logging for Troubleshooting

   Write logs that help you find problems in a running application.

   Show 5 topics
   • What to log at each level
   • Parameterised log messages
   • Request ids to trace one request
   • Logback configuration and log files
   • What never to log

8. 18.8Code Quality & Clean Code

   Keep code easy to read and change as the project grows.

   Show 6 topics
   • Naming, small methods and clear intent
   • Code smells: duplication, long methods, god classes
   • Safe refactoring with tests and IDE tools
   • Code coverage with JaCoCo and what it does not tell you
   • Static analysis with SonarLint
   • Code review checklist

9. 18.9Testing Mini Project: Test ShopLite

   Add unit, slice and integration tests to ShopLite and fix the bugs they find.

   Show 5 topics
   • Unit tests for pricing and order rules
   • Controller tests for validation and errors
   • Repository tests for custom queries
   • Security tests for roles and ownership
   • Coverage report and a refactoring pass