cuioss/junit-core

JUnit Core Skill

REFERENCE MODE: This skill provides reference material. Load specific standards on-demand based on current task.

JUnit 5 testing standards for general Java projects. This skill covers test structure, naming conventions, coverage requirements, and the AAA (Arrange-Act-Assert) pattern.

Prerequisites

This skill applies to Java projects using JUnit 5:

• org.junit.jupiter:junit-jupiter (JUnit 5)

Workflow

Step 1: Load Core Testing Standards

Important: Load this standard for any testing work.

Read: standards/testing-junit-core.md

This provides foundational rules for:

• Test class requirements (at least one per production class, splitting at 200+ lines)
• AAA pattern with generated test data (no literals, no phase comments)
• Full JUnit 5 assertion API (assertAll, assertInstanceOf, assertDoesNotThrow)
• @Nested for grouping (3+ related tests)
• Corner case testing
• Coverage requirements (80% line/branch minimum)

Step 2: Load Additional Standards (As Needed)

Integration Testing (load for IT work):

Read: standards/testing-integration.md

Use when: Writing or reviewing integration tests (*IT.java). Covers naming, separation, and lifecycle.

Async Testing (load for async/concurrent code):

Read: standards/testing-async-patterns.md

Use when: Testing asynchronous behavior. Covers Awaitility patterns (never Thread.sleep).

Coverage Analysis (load for coverage work):

Read: standards/coverage-analysis-pattern.md

Use when: Analyzing test coverage or improving coverage metrics.

Key Rules Summary

Test Class Requirements

// CORRECT - At least one test class per production class
// TokenValidator.java → TokenValidatorTest.java
// UserService.java → UserServiceTest.java

AAA Pattern — No Phase Comments

@Test
@DisplayName("Should validate token with correct issuer")
void shouldValidateTokenWithCorrectIssuer() {
    var issuer = Generators.nonBlankStrings().next();
    var token = createTokenWithIssuer(issuer);

    var result = validator.validate(token);

    assertTrue(result.isValid(), "Token should be valid");
    assertEquals(issuer, result.getIssuer(), "Issuer should match");
}

Grouped Assertions with assertAll

@Test
@DisplayName("Should parse all token claims")
void shouldParseAllTokenClaims() {
    var token = createValidToken();

    var claims = parser.parse(token);

    assertAll("Token claims",
        () -> assertNotNull(claims.getSubject(), "Subject should be present"),
        () -> assertInstanceOf(Instant.class, claims.getExpiry(), "Expiry should be Instant"),
        () -> assertFalse(claims.getRoles().isEmpty(), "Roles should not be empty")
    );
}

Coverage Requirements

• Minimum 80% line coverage
• Minimum 80% branch coverage
• Critical/hot paths: near 100% coverage
• All public APIs must be tested

Related Skills

• plan-marshall:dev-general-module-testing - Language-agnostic testing principles
• pm-dev-java:junit-integration - Maven integration testing
• pm-dev-java-cui:cui-testing - CUI test generator framework
• pm-dev-java:java-core - Core Java patterns

Templates

Unit test class — starting point for new test classes:

Read: templates/unit-test-class.java.tmpl

Replace ${PACKAGE}, ${CLASS_UNDER_TEST}, ${METHOD_1}, and placeholder comments with actual values.

Standards Reference

| Standard | Purpose | |----------|---------| | testing-junit-core.md | Test structure, AAA pattern, assertions, nesting | | testing-integration.md | Integration test naming, separation, lifecycle | | testing-async-patterns.md | Awaitility patterns (never Thread.sleep) | | coverage-analysis-pattern.md | Coverage analysis and gap improvement |