TDD Skill

Automates Test Driven Development workflows for Java Spring Boot projects.

Quick Start: Coverage Analysis

Generate and check coverage (no scripts needed):

# 1. Run tests with coverage
mvn test jacoco:report -q

# 2. Overall coverage
awk -F',' 'NR>1{ic+=$5;im+=$4}END{printf "%.1f%%\n",ic*100/(ic+im)}' target/site/jacoco/jacoco.csv

# 3. Classes below 95%
awk -F',' 'NR>1 && $4+$5>0{pct=$5*100/($4+$5);if(pct<95)printf "%.1f%% %s.%s (%d lines)\n",pct,$2,$3,$8}' target/site/jacoco/jacoco.csv | sort -n

# 4. Specific class
grep "ClassName" target/site/jacoco/jacoco.csv | awk -F',' '{printf "%.1f%%\n",$5*100/($4+$5)}'

CSV columns: INSTRUCTION_MISSED($4), INSTRUCTION_COVERED($5), LINE_MISSED($8), LINE_COVERED($9)

Red-Green-Refactor Cycle

1. RED - Write Failing Test

# Generate test scaffold
./scripts/generate-test-scaffold.sh UserService service

# Write test, run to verify it fails
mvn test -Dtest=UserServiceTest

2. GREEN - Make Test Pass

# Implement minimal code to pass

# Run test to verify
mvn test -Dtest=UserServiceTest

3. REFACTOR - Improve Code

# Refactor while keeping tests green

# Verify all tests pass
mvn test

# Check coverage
mvn test jacoco:report -q && \
awk -F',' 'NR>1{ic+=$5;im+=$4}END{printf "Coverage: %.1f%%\n",ic*100/(ic+im)}' target/site/jacoco/jacoco.csv

Test Types

Unit Test:

• Location: src/test/java/{package}/{ClassName}Test.java
• Uses: @ExtendWith(MockitoExtension.class), @Mock, @InjectMocks
• Tests: Single component in isolation

Integration Test:

• Location: src/test/java/{package}/{ClassName}IntegrationTest.java
• Extends: AbstractIntegrationTest
• Uses: @SpringBootTest, Testcontainers for real DB
• Tests: Components working together

Test Naming Convention

@Test
void shouldReturnUserWhenValidIdProvided() { }

@Test
void shouldThrowExceptionWhenUserNotFound() { }

Pattern: should{ExpectedBehavior}When{Condition}

Test Structure (Given-When-Then)

@Test
void shouldCalculateTotalPrice() {
    // Given - Setup test data
    var item = new Item("Widget", 10.00);
    var quantity = 3;
    
    // When - Execute behavior
    var total = calculator.calculateTotal(item, quantity);
    
    // Then - Verify outcome
    assertThat(total).isEqualTo(30.00);
}

Coverage Targets

• Service Layer: 90%+
• Critical Logic: 100%
• Integration Tests: All API endpoints

Layer-specific coverage:

# Services
grep "\.service\." target/site/jacoco/jacoco.csv | awk -F',' '{ic+=$5;im+=$4}END{printf "%.1f%%\n",ic*100/(ic+im)}'

# Controllers
grep "\.controller\." target/site/jacoco/jacoco.csv | awk -F',' '{ic+=$5;im+=$4}END{printf "%.1f%%\n",ic*100/(ic+im)}'

Scripts Available

Optional - use direct commands above for simpler workflow

• scripts/discover-test-patterns.sh - Analyze existing test patterns
• scripts/generate-test-scaffold.sh <ComponentName> <type> [unit|integration] - Create test file
• scripts/run-targeted-tests.sh <TestPattern> - Run specific tests
• scripts/analyze-coverage.sh [target] - Coverage report (wraps JaCoCo)

Common Workflows

New REST Endpoint:

# 1. Write integration test (should fail - 404)
./scripts/generate-test-scaffold.sh UserController controller integration

# 2. Implement endpoint (test passes - 201)
# 3. Write service unit tests
# 4. Verify coverage
mvn test jacoco:report -q && grep "UserService" target/site/jacoco/jacoco.csv

Add Business Logic:

# 1. Write unit test for rule (fails)
# 2. Implement logic (passes)
# 3. Add edge cases
# 4. Check coverage

Best Practices

✅ Write tests before implementation (Red phase) ✅ Test one behavior per test method ✅ Use descriptive test names ✅ Keep tests fast and focused ✅ Mock external dependencies in unit tests ✅ Use real DB (Testcontainers) in integration tests

❌ Don't skip Red phase (verify test fails first) ❌ Don't test implementation details (test behavior) ❌ Don't create interdependent tests ❌ Don't commit with failing tests

Complex Analysis (Python)

When awk isn't sufficient:

python3 << 'EOF'
import csv
with open('target/site/jacoco/jacoco.csv') as f:
    rows = list(csv.DictReader(f))
    covered = sum(int(r['INSTRUCTION_COVERED']) for r in rows)
    missed = sum(int(r['INSTRUCTION_MISSED']) for r in rows)
    total = covered + missed
    print(f"Coverage: {covered}/{total} ({covered*100/total:.1f}%)")
    
    gaps = [(int(r['INSTRUCTION_MISSED']), f"{r['PACKAGE']}.{r['CLASS']}", int(r['LINE_MISSED']))
            for r in rows if int(r['INSTRUCTION_MISSED']) > 0]
    for m, cls, lines in sorted(gaps, reverse=True)[:5]:
        print(f"  {cls}: {lines} lines missing")
EOF

Maven Integration

# Run tests
mvn test

# Run specific test
mvn test -Dtest=UserServiceTest

# With coverage
mvn test jacoco:report

# Skip tests (not recommended in TDD!)
mvn clean package -DskipTests

References

See Agent Skills Specification for format details.