golang-testing

name	golang-testing
description	Go testing patterns including table-driven tests, subtests, benchmarks, fuzzing, and test coverage. Follows TDD methodology with idiomatic Go practices.

Go Testing Patterns

Comprehensive Go testing patterns for writing reliable, maintainable tests following TDD methodology.

When to Activate

• Writing new Go functions or methods
• Adding test coverage to existing code
• Creating benchmarks for performance-critical code
• Implementing fuzz tests for input validation
• Following TDD workflow in Go projects

TDD Workflow for Go

The RED-GREEN-REFACTOR Cycle

RED     → Write a failing test first
GREEN   → Write minimal code to pass the test
REFACTOR → Improve code while keeping tests green
REPEAT  → Continue with next requirement

For detailed step-by-step examples, see references/code-examples.md.

Table-Driven Tests

The standard pattern for Go tests. Enables comprehensive coverage with minimal code.

func TestAdd(t *testing.T) {
    tests := []struct {
        name     string
        a, b     int
        expected int
    }{
        {"positive numbers", 2, 3, 5},
        {"negative numbers", -1, -2, -3},
        {"zero values", 0, 0, 0},
        {"mixed signs", -1, 1, 0},
        {"large numbers", 1000000, 2000000, 3000000},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got := Add(tt.a, tt.b)
            if got != tt.expected {
                t.Errorf("Add(%d, %d) = %d; want %d",
                    tt.a, tt.b, got, tt.expected)
            }
        })
    }
}

See references/code-examples.md for error handling patterns and advanced error case testing.

Subtests and Sub-benchmarks

Organizing Related Tests

func TestUser(t *testing.T) {
    // Setup shared by all subtests
    db := setupTestDB(t)

    t.Run("Create", func(t *testing.T) {
        user := &User{Name: "Alice"}
        err := db.CreateUser(user)
        if err != nil {
            t.Fatalf("CreateUser failed: %v", err)
        }
        if user.ID == "" {
            t.Error("expected user ID to be set")
        }
    })

    t.Run("Get", func(t *testing.T) {
        user, err := db.GetUser("alice-id")
        if err != nil {
            t.Fatalf("GetUser failed: %v", err)
        }
        if user.Name != "Alice" {
            t.Errorf("got name %q; want %q", user.Name, "Alice")
        }
    })

    t.Run("Update", func(t *testing.T) {
        // ...
    })

    t.Run("Delete", func(t *testing.T) {
        // ...
    })
}

Parallel Subtests

func TestParallel(t *testing.T) {
    tests := []struct {
        name  string
        input string
    }{
        {"case1", "input1"},
        {"case2", "input2"},
        {"case3", "input3"},
    }

    for _, tt := range tests {
        tt := tt // Capture range variable
        t.Run(tt.name, func(t *testing.T) {
            t.Parallel() // Run subtests in parallel
            result := Process(tt.input)
            // assertions...
            _ = result
        })
    }
}

Test Helpers

Helper Functions

func setupTestDB(t *testing.T) *sql.DB {
    t.Helper() // Marks this as a helper function

    db, err := sql.Open("sqlite3", ":memory:")
    if err != nil {
        t.Fatalf("failed to open database: %v", err)
    }

    // Cleanup when test finishes
    t.Cleanup(func() {
        db.Close()
    })

    // Run migrations
    if _, err := db.Exec(schema); err != nil {
        t.Fatalf("failed to create schema: %v", err)
    }

    return db
}

func assertNoError(t *testing.T, err error) {
    t.Helper()
    if err != nil {
        t.Fatalf("unexpected error: %v", err)
    }
}

func assertEqual[T comparable](t *testing.T, got, want T) {
    t.Helper()
    if got != want {
        t.Errorf("got %v; want %v", got, want)
    }
}

Temporary Files and Directories

func TestFileProcessing(t *testing.T) {
    // Create temp directory - automatically cleaned up
    tmpDir := t.TempDir()

    // Create test file
    testFile := filepath.Join(tmpDir, "test.txt")
    err := os.WriteFile(testFile, []byte("test content"), 0644)
    if err != nil {
        t.Fatalf("failed to create test file: %v", err)
    }

    // Run test
    result, err := ProcessFile(testFile)
    if err != nil {
        t.Fatalf("ProcessFile failed: %v", err)
    }

    // Assert...
    _ = result
}

Golden Files Pattern

Golden files are reference outputs stored in testdata/ for testing against known-good results. Use go test -args -update to refresh them when behavior changes intentionally. See references/code-examples.md for full implementation.

Mocking with Interfaces

Use interfaces for dependency injection and create mock implementations for tests:

• Define dependencies as interfaces
• Create production implementations
• Create mock implementations with function fields for tests
• Inject mocks into code under test

See references/code-examples.md for complete mock examples.

Benchmarks

Basic Benchmarks

func BenchmarkProcess(b *testing.B) {
    data := generateTestData(1000)
    b.ResetTimer() // Don't count setup time

    for i := 0; i < b.N; i++ {
        Process(data)
    }
}

// Run: go test -bench=BenchmarkProcess -benchmem
// Output: BenchmarkProcess-8   10000   105234 ns/op   4096 B/op   10 allocs/op

Use b.Run() for sub-benchmarks with different sizes or configurations. See references/code-examples.md for examples comparing multiple approaches.

Memory Allocation Optimization

Compare allocation strategies with -benchmem flag. See references/code-examples.md for detailed memory allocation comparison examples.

Fuzzing (Go 1.18+)

Basic Fuzz Test

func FuzzParseJSON(f *testing.F) {
    // Add seed corpus
    f.Add(`{"name": "test"}`)
    f.Add(`{"count": 123}`)
    f.Add(`[]`)
    f.Add(`""`)

    f.Fuzz(func(t *testing.T, input string) {
        var result map[string]interface{}
        err := json.Unmarshal([]byte(input), &result)

        if err != nil {
            // Invalid JSON is expected for random input
            return
        }

        // If parsing succeeded, re-encoding should work
        _, err = json.Marshal(result)
        if err != nil {
            t.Errorf("Marshal failed after successful Unmarshal: %v", err)
        }
    })
}

// Run: go test -fuzz=FuzzParseJSON -fuzztime=30s

Add seed corpus with f.Add() and verify properties that must always hold true. For multiple input parameters and property validation, see references/code-examples.md.

Test Coverage

Running Coverage

# Basic coverage
go test -cover ./...

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

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

# View coverage by function
go tool cover -func=coverage.out

# Coverage with race detection
go test -race -coverprofile=coverage.out ./...

Coverage Targets

Code Type	Target
Critical business logic	100%
Public APIs	90%+
General code	80%+
Generated code	Exclude

Excluding Generated Code from Coverage

//go:generate mockgen -source=interface.go -destination=mock_interface.go

// In coverage profile, exclude with build tags:
// go test -cover -tags=!generate ./...

HTTP Handler Testing

Use httptest.NewRequest() and httptest.NewRecorder() for testing handlers without starting a server. Combine with table-driven tests for comprehensive coverage of different HTTP methods, paths, and response codes. See references/code-examples.md for full examples.

Testing Commands

# Run all tests
go test ./...

# Run tests with verbose output
go test -v ./...

# Run specific test
go test -run TestAdd ./...

# Run tests matching pattern
go test -run "TestUser/Create" ./...

# Run tests with race detector
go test -race ./...

# Run tests with coverage
go test -cover -coverprofile=coverage.out ./...

# Run short tests only
go test -short ./...

# Run tests with timeout
go test -timeout 30s ./...

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

# Run fuzzing
go test -fuzz=FuzzParse -fuzztime=30s ./...

# Count test runs (for flaky test detection)
go test -count=10 ./...

Best Practices

Effective Patterns:

• Write tests first (TDD)
• Use table-driven tests for comprehensive coverage
• Test behavior, not implementation
• Use t.Helper() in helper functions
• Use t.Parallel() for independent tests
• Clean up resources with t.Cleanup()
• Use meaningful test names that describe the scenario
• Test error paths thoroughly
• Prefer integration tests over mocking when possible

Avoid:

• Testing private functions directly (test through public API)
• Using time.Sleep() in tests (use channels or conditions)
• Leaving flaky tests unfixed or unremoved
• Over-mocking instead of testing real behavior

Integration with CI/CD

See references/code-examples.md for a GitHub Actions CI/CD example with coverage validation.