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junit skill

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This skill helps you write and configure JUnit tests with annotations, assertions, and best practices for Java projects.

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SKILL.md
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---
name: junit
description: Provides comprehensive guidance for JUnit testing framework including test annotations, assertions, test lifecycle, and best practices. Use when the user asks about JUnit, needs to write Java unit tests, use JUnit annotations, or configure JUnit for Java projects.
license: Complete terms in LICENSE.txt
---

## When to use this skill

Use this skill whenever the user wants to:
- [待完善：根据具体工具添加使用场景]

## How to use this skill

[待完善：根据具体工具添加使用指南]

## Best Practices

[待完善：根据具体工具添加最佳实践]

## Keywords

[待完善：根据具体工具添加关键词]

Overview

This skill delivers practical, hands-on guidance for using the JUnit testing framework in Java projects. It covers core annotations, assertions, test lifecycle methods, parameterized tests, and integration tips for build tools and IDEs. The focus is on writing clear, maintainable unit tests and configuring JUnit for common project setups. Use it to quickly resolve testing questions or improve test quality.

How this skill works

The skill inspects common JUnit topics and provides targeted advice: which annotations to use (@Test, @BeforeEach, @AfterAll, @Nested, @Disabled), how assertions and assumptions work, and when to write parameterized or repeated tests. It explains lifecycle hooks, exception and timeout testing patterns, and best practices for test isolation and mocking. The guidance includes configuration notes for Maven, Gradle, and popular IDEs, plus troubleshooting tips for flaky tests.

When to use it

  • You need to write or refactor Java unit tests with JUnit 4 or JUnit 5.
  • You want to learn correct usage of JUnit annotations and lifecycle methods.
  • You need examples for assertions, exception testing, or parameterized tests.
  • You are configuring JUnit in Maven or Gradle or integrating with CI pipelines.
  • You want to diagnose flaky or slow tests and improve test isolation.

Best practices

  • Favor small, focused tests that assert one behavior per test method.
  • Use @BeforeEach/@AfterEach for test setup and teardown; reserve @BeforeAll/@AfterAll for expensive shared resources.
  • Prefer explicit assertions with helpful messages; avoid over-reliance on try/catch for exception tests—use assertThrows.
  • Keep tests fast and deterministic: mock external dependencies, use in-memory stores, and avoid real network or file I/O when possible.
  • Group related tests with @Nested and use descriptive method names to document intent.

Example use cases

  • Show example test class demonstrating @BeforeEach, @AfterEach, and multiple @Test methods.
  • Convert an existing integration-style test into focused unit tests with mocks and assertThrows for exceptions.
  • Create a parameterized test for validating multiple input cases with @ParameterizedTest and @CsvSource.
  • Configure Maven surefire and Gradle test tasks to run JUnit 5 and include test reports for CI.
  • Diagnose a flaky test by isolating shared state and replacing static singletons with injectable collaborators.

FAQ

Which JUnit version should I use?

Prefer JUnit 5 for new projects; it offers a richer extension model and clearer annotations. Use JUnit Vintage to run legacy JUnit 4 tests if needed.

How do I test exceptions in JUnit?

Use assertThrows to verify exceptions and capture the thrown instance for further assertions instead of try/catch idioms.

How to speed up slow tests?

Avoid external systems, use mocks or lightweight in-memory implementations, parallelize tests where safe, and minimize per-test expensive setup.