tdd-guide

TDD Guide

Test-driven development skill for generating tests, analyzing coverage, and guiding red-green-refactor workflows. Adapted from alirezarezvani/claude-skills for JUnit 5 and the jhelm project.

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Workflows

Generate Tests from Code

1. Provide source code (Java class or method)
2. Target framework: JUnit 5 (org.junit.jupiter.api)
3. Follow jhelm conventions:
   • Use Assertions (not AssertJ)
   • Use @TempDir for temporary files
   • Use @ParameterizedTest with @CsvSource or @MethodSource to avoid duplication
   • Prefer real test data over Mockito mocks
   • Mockito acceptable only for HTTP (CloseableHttpClient) and Kubernetes (KubeService)
4. Validation: Tests compile and cover happy path, error cases, edge cases

Analyze Coverage Gaps

1. Run JaCoCo: ./mvnw test (generates target/site/jacoco/jacoco.xml)
2. Use /jacoco skill to analyze coverage by module
3. Prioritize gaps:
   • P0: 0% covered classes with many lines (high impact)
   • P1: Partially covered classes with uncovered branches
   • P2: Low-risk utility classes
4. Generate tests for P0 items first
5. Target: 80% minimum coverage per module

TDD New Feature

1. Write failing test first (RED)
2. Run: ./mvnw test -Dtest=NewFeatureTest -pl <module>
3. Implement minimal code to pass (GREEN)
4. Run test again to confirm pass
5. Refactor while keeping tests green (REFACTOR)
6. Run ./mvnw validate to verify formatting + PMD + checkstyle

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JUnit 5 Patterns for jhelm

Basic Test

@Test
void testChartLoadingFromDirectory() throws Exception {
	Chart chart = ChartLoader.load(Path.of("src/test/resources/test-charts/minimal"));
	assertEquals("minimal", chart.getMetadata().getName());
	assertNotNull(chart.getValues());
}

Parameterized Test (avoid duplication)

@ParameterizedTest
@CsvSource(delimiter = '|', value = {
	"upper     | hello | HELLO",
	"lower     | HELLO | hello",
	"title     | hello world | Hello World"
})
void testStringFunctions(String func, String input, String expected)
		throws IOException, TemplateException {
	assertEquals(expected, exec("{{ " + func + " \"" + input + "\" }}"));
}