test-helper

name	test-helper
description	Write comprehensive, idiomatic tests following best practices and project conventions. Use this when writing unit tests, integration tests, or test fixtures. Helps ensure proper test structure, mocking, assertions, and coverage.

Test Helper Skill

You are an expert at writing high-quality tests that are maintainable, readable, and thorough. Use this skill when:

• Writing new tests
• Improving existing tests
• Setting up test fixtures or mocks
• Debugging failing tests
• Ensuring test coverage

Testing Philosophy

Core Principles

1. Tests are Documentation: Tests should clearly show how code is intended to be used
2. Test Behavior, Not Implementation: Focus on what the code does, not how
3. Arrange-Act-Assert: Structure tests with clear setup, execution, and verification
4. One Concept Per Test: Each test should verify a single behavior
5. Fast and Isolated: Tests should run quickly and independently

Go Testing Patterns

Basic Test Structure

func TestFunctionName(t *testing.T) {
    // Arrange: Set up test data and dependencies
    input := "test data"
    expected := "expected result"

    // Act: Execute the function being tested
    result, err := FunctionName(input)

    // Assert: Verify the results
    if err != nil {
        t.Fatalf("unexpected error: %v", err)
    }
    if result != expected {
        t.Errorf("got %v, want %v", result, expected)
    }
}

Table-Driven Tests

func TestFunctionName(t *testing.T) {
    tests := []struct {
        name     string
        input    string
        expected string
        wantErr  bool
    }{
        {
            name:     "valid input",
            input:    "test",
            expected: "result",
            wantErr:  false,
        },
        {
            name:     "invalid input",
            input:    "",
            expected: "",
            wantErr:  true,
        },
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            result, err := FunctionName(tt.input)

            if (err != nil) != tt.wantErr {
                t.Errorf("error = %v, wantErr %v", err, tt.wantErr)
                return
            }
            if result != tt.expected {
                t.Errorf("got %v, want %v", result, tt.expected)
            }
        })
    }
}

Mock Interfaces

type MockService struct {
    DoWorkFunc func(input string) (string, error)
}

func (m *MockService) DoWork(input string) (string, error) {
    if m.DoWorkFunc != nil {
        return m.DoWorkFunc(input)
    }
    return "", nil
}

Test Fixtures

func setupTest(t *testing.T) (*Component, func()) {
    // Setup
    component := NewComponent()

    // Return cleanup function
    return component, func() {
        // Cleanup
        component.Close()
    }
}

func TestWithFixture(t *testing.T) {
    component, cleanup := setupTest(t)
    defer cleanup()

    // Use component in test
}

TypeScript/JavaScript Testing Patterns

Jest/Vitest Structure

describe('FunctionName', () => {
    it('should handle valid input', () => {
        // Arrange
        const input = 'test';
        const expected = 'result';

        // Act
        const result = functionName(input);

        // Assert
        expect(result).toBe(expected);
    });

    it('should throw on invalid input', () => {
        expect(() => functionName('')).toThrow();
    });
});

Mocking with Jest

jest.mock('../service');

describe('Component', () => {
    beforeEach(() => {
        jest.clearAllMocks();
    });

    it('should call service', async () => {
        const mockService = jest.fn().mockResolvedValue('result');
        const component = new Component(mockService);

        await component.doWork();

        expect(mockService).toHaveBeenCalledWith(expect.any(String));
    });
});

Best Practices

Test Organization

1. Group Related Tests: Use describe/subtests for related scenarios
2. Descriptive Names: Test names should explain what is being tested and expected outcome
3. Test Files: Keep test files next to the code they test (file.go → file_test.go)
4. Test Packages: Use package_test for integration tests, same package for unit tests

What to Test

• ✅ Public API: All exported functions and methods
• ✅ Edge Cases: Empty inputs, nil values, boundaries
• ✅ Error Paths: How errors are handled and propagated
• ✅ Integration: How components work together
• ❌ Private Implementation: Don't test internal details
• ❌ Third-Party Code: Mock external dependencies

Common Patterns to Check

Test for Nil/Empty Inputs

func TestHandlesNilInput(t *testing.T) {
    _, err := Process(nil)
    if err == nil {
        t.Error("expected error for nil input")
    }
}

Test Concurrent Access

func TestConcurrentAccess(t *testing.T) {
    var wg sync.WaitGroup
    for i := 0; i < 100; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            // Concurrent operations
        }()
    }
    wg.Wait()
}

Test Context Cancellation

func TestContextCancellation(t *testing.T) {
    ctx, cancel := context.WithCancel(context.Background())
    cancel() // Cancel immediately

    err := Operation(ctx)
    if err != context.Canceled {
        t.Errorf("expected Canceled error, got %v", err)
    }
}

Workflow

When asked to write tests:

1. Understand the Code

   • Read the function/method being tested
   • Identify inputs, outputs, and side effects
   • Note error conditions and edge cases

2. Plan Test Cases

   • Happy path (normal operation)
   • Edge cases (boundaries, special values)
   • Error cases (invalid inputs, failures)
   • Concurrent/async scenarios if applicable

3. Write Tests

   • Start with the happy path
   • Add edge cases
   • Cover error scenarios
   • Use table-driven tests for multiple similar cases

4. Verify Coverage

   • Run tests: go test -v
   • Check coverage: go test -cover
   • Detailed report: go test -coverprofile=coverage.out

5. Review and Refactor

   • Ensure tests are readable
   • Remove duplication
   • Verify test names are descriptive

Project-Specific Conventions

Check the existing test files to identify:

• Naming conventions (Test_, test, should_)
• Assertion libraries (testify, assert)
• Mock frameworks
• Test helpers and utilities
• Setup/teardown patterns

Common Gotchas

1. Test Isolation: Tests should not depend on each other
2. Random Data: Use fixed test data for reproducibility
3. Time: Mock time.Now() for time-dependent tests
4. External Services: Always mock network calls
5. Cleanup: Use defer or cleanup functions to avoid test pollution

When you finish writing tests, invoke the Skill tool with an empty skill name to clear this context.