Go Testing Patterns

This skill provides professional testing patterns for Go applications, focusing on maintainability, coverage, and CI integration.

When to Use

•Writing unit tests for Go packages
•Mocking external dependencies (databases, APIs, shells)
•Setting up CI/CD pipelines with test coverage
•Creating integration tests with build tags

Core Patterns

1. Table-Driven Tests

The preferred pattern for testing multiple scenarios:

func TestValidateInput(t *testing.T) {
    tests := []struct {
        name    string
        input   string
        want    bool
        wantErr bool
    }{
        {
            name:  "valid input",
            input: "hello",
            want:  true,
        },
        {
            name:    "empty input",
            input:   "",
            wantErr: true,
        },
        {
            name:  "special characters",
            input: "hello-world_123",
            want:  true,
        },
        {
            name:    "invalid characters",
            input:   "hello;drop",
            wantErr: true,
        },
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got, err := ValidateInput(tt.input)
            
            if (err != nil) != tt.wantErr {
                t.Errorf("ValidateInput() error = %v, wantErr %v", err, tt.wantErr)
                return
            }
            
            if got != tt.want {
                t.Errorf("ValidateInput() = %v, want %v", got, tt.want)
            }
        })
    }
}

2. Interface-Based Mocking

Define interfaces for external dependencies to enable mocking:

// In production code
type DataStore interface {
    Get(id string) (*Item, error)
    Save(item *Item) error
}

type Service struct {
    store DataStore
}

// In test code
type MockDataStore struct {
    GetFunc  func(id string) (*Item, error)
    SaveFunc func(item *Item) error
}

func (m *MockDataStore) Get(id string) (*Item, error) {
    if m.GetFunc != nil {
        return m.GetFunc(id)
    }
    return nil, nil
}

func (m *MockDataStore) Save(item *Item) error {
    if m.SaveFunc != nil {
        return m.SaveFunc(item)
    }
    return nil
}

// Usage in tests
func TestService_GetItem(t *testing.T) {
    mock := &MockDataStore{
        GetFunc: func(id string) (*Item, error) {
            return &Item{ID: id, Name: "Test"}, nil
        },
    }

    service := &Service{store: mock}
    item, err := service.GetItem("123")

    if err != nil {
        t.Fatalf("unexpected error: %v", err)
    }
    if item.Name != "Test" {
        t.Errorf("expected Name 'Test', got '%s'", item.Name)
    }
}

3. Test Helpers

Create reusable test helpers:

// testhelpers_test.go

// Helper to create test items
func makeTestItem(t *testing.T, name string) *Item {
    t.Helper()
    return &Item{
        ID:        uuid.New().String(),
        Name:      name,
        CreatedAt: time.Now(),
    }
}

// Helper for comparing errors
func assertError(t *testing.T, got, want error) {
    t.Helper()
    if got == nil && want != nil {
        t.Errorf("expected error %v, got nil", want)
        return
    }
    if got != nil && want == nil {
        t.Errorf("unexpected error: %v", got)
        return
    }
    if got != nil && want != nil && !errors.Is(got, want) {
        t.Errorf("expected error %v, got %v", want, got)
    }
}

// Helper for cleanup
func setupTestEnv(t *testing.T) func() {
    t.Helper()
    // Setup...
    return func() {
        // Cleanup...
    }
}

4. Build Tags for Integration Tests

Separate unit tests from integration tests:

//go:build integration
// +build integration

package mypackage

import (
    "testing"
)

func TestIntegration_RealDatabase(t *testing.T) {
    if testing.Short() {
        t.Skip("skipping integration test in short mode")
    }
    // Real database tests here
}

Run with: go test -tags=integration ./...

5. Windows-Specific Tests

For Windows-only functionality:

//go:build windows
// +build windows

package hyperv

import (
    "testing"
)

func TestHyperV_ListVMs(t *testing.T) {
    // This test only runs on Windows
}

6. Test Main for Setup/Teardown

func TestMain(m *testing.M) {
    // Setup before all tests
    setup()
    
    // Run all tests
    code := m.Run()
    
    // Teardown after all tests
    teardown()
    
    os.Exit(code)
}

func setup() {
    // Initialize resources
}

func teardown() {
    // Clean up resources
}

Coverage Commands

bash

# Run tests with coverage
go test -v -cover ./...

# Generate coverage profile
go test -coverprofile=coverage.out ./...

# View coverage in browser
go tool cover -html=coverage.out

# Get coverage percentage
go test -cover ./... | grep coverage

# Coverage for specific package with detailed output
go test -v -coverprofile=coverage.out -covermode=atomic ./mypackage/...

Makefile Integration

makefile

.PHONY: test test-coverage test-integration

test: ## Run unit tests
	go test -v ./...

test-coverage: ## Run tests with coverage report
	go test -v -cover ./...
	go test -coverprofile=coverage.out ./...
	go tool cover -html=coverage.out -o coverage.html
	@echo "Coverage report: coverage.html"

test-integration: ## Run integration tests
	go test -v -tags=integration ./...

test-short: ## Run quick tests only
	go test -v -short ./...

bench: ## Run benchmarks
	go test -bench=. -benchmem ./...

GitHub Actions CI

yaml

name: Tests

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  test:
    runs-on: windows-latest  # or ubuntu-latest
    
    steps:
    - uses: actions/checkout@v4

    - name: Set up Go
      uses: actions/setup-go@v5
      with:
        go-version: '1.21'

    - name: Cache Go modules
      uses: actions/cache@v4
      with:
        path: |
          ~/go/pkg/mod
          ~/.cache/go-build
        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
        restore-keys: |
          ${{ runner.os }}-go-

    - name: Run tests
      run: go test -v ./...

    - name: Run tests with coverage
      run: go test -v -coverprofile=coverage.out -covermode=atomic ./...

    - name: Upload coverage
      uses: codecov/codecov-action@v5
      with:
        files: ./coverage.out
        fail_ci_if_error: false

Best Practices

•
Name tests descriptively: TestFunction_Scenario_ExpectedResult
•
Use t.Helper() in helper functions for better error reporting
•
Avoid test pollution: Each test should be independent

•

Use t.Parallel() for parallel execution when safe:

func TestParallel(t *testing.T) {
    t.Parallel()
    // Test code
}

•
Keep tests fast: Unit tests should run in milliseconds
•
Test error paths: Don't just test happy paths

•

Use meaningful assertions:

// ❌ Bad
if result != expected {
    t.Fail()
}

// ✅ Good
if result != expected {
    t.Errorf("got %v, want %v", result, expected)
}

•
Test behavior, not implementation: Focus on what the function does, not how

Common Patterns for Mocking

Mock with Call Tracking

type MockService struct {
    Calls     []string
    ReturnVal interface{}
    ReturnErr error
}

func (m *MockService) DoSomething(id string) error {
    m.Calls = append(m.Calls, "DoSomething:"+id)
    return m.ReturnErr
}

// In test
func TestTrackCalls(t *testing.T) {
    mock := &MockService{}
    // ... run code ...
    
    if len(mock.Calls) != 2 {
        t.Errorf("expected 2 calls, got %d", len(mock.Calls))
    }
}

Mock with Sequence of Returns

type SequenceMock struct {
    Returns []interface{}
    Index   int
}

func (m *SequenceMock) Next() interface{} {
    if m.Index >= len(m.Returns) {
        return nil
    }
    val := m.Returns[m.Index]
    m.Index++
    return val
}