# Java Testing

> Testing standards using JUnit 5, AssertJ, Mockito, Cucumber, and Spring Boot integration tests for Java. Use when writing or reviewing Java test behavior, including parallel execution and BDD; defer Kotlin-only tests, virtual-thread test infrastructure, and coverage-report/tooling configuration.

- Skill: `hoangnguyen0403/java-testing` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add hoangnguyen0403/java-testing`
- Raw SKILL.md: https://api.skillmd.com/api/skills/hoangnguyen0403/java-testing/raw
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- Category: Docs & Writing
- Author: HoangNguyen0403 (https://skillmd.com/u/hoangnguyen0403)
- Updated: 2026-08-19
- Page: https://skillmd.com/skills/hoangnguyen0403/java-testing

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# Java Testing Standards

## **Priority: P0 (CRITICAL)**


## Implementation Guidelines

- **JUnit 5 (Jupiter)**: Use **`@Test`**, **`@BeforeEach`**, and **`@AfterEach`**. Avoid JUnit 4 classes.
- **Fluent Assertions**: Use **`AssertJ (assertThat)`** over JUnit `assertEquals` — enhanced readability.
- **Naming**: Use **`MethodName_State_Result`** or **`@DisplayName("Check if X when Y")`**.
- **Parameterized Tests**: Use **`@ParameterizedTest`** with **`@ValueSource`**, **`@CsvSource`**, or **`@MethodSource`**.
- **Mocking Strategy**: Use **`Mockito`** with `@ExtendWith(MockitoExtension.class)` (JUnit 5). Use **`@Mock`**, **`@Spy`**, and **`@InjectMocks`**. NEVER mock data-only Records.
- **Integration Testing**: Use **`Testcontainers`** with `@Container` annotation for real databases (PostgreSQL/Redis) in integration tests (`*IT.java`).
- **Isolation**: Each test method MUST isolated and independent; use **`@DirtiesContext`** sparingly.
- **AssertJ Chaining**: Chain assertions for clarity: **`assertThat(result).isNotNull().hasSize(2).contains("X")`**.
- **Mocking verification**: Use **`verify(mock, times(1)).method()`** to audit side-effects.
- **Exceptions**: Use **`assertThatThrownBy(() -> ...)`** to verify specific Exception types and messages.

## Anti-Patterns

- **No Logic in Tests**: Keep tests declarative; no loops or if/else branching.
- **No System.out in Tests**: Use assertions; never print to stdout.
- **No Legacy Assertions**: Use `assertThat(a).isEqualTo(b)`, not `assertTrue(a == b)`.
- **No Shared State**: Tests must isolated and order-independent.

## References

- [Full JUnit 5 + Mockito + AssertJ Template](references/junit-template.md)