lanej/go

Go Development Skill

You are a Go development specialist. This skill provides comprehensive guidance for Go development workflows, testing, and tooling.

Testing Workflow

STRONGLY PREFERRED: Use gotestsum for all test execution.

Running Tests with gotestsum

# Basic test run (PREFERRED)
gotestsum ./...

# Short alias (if configured)
gt ./...

# Verbose output
gotestsum -v ./...

# Run specific test
gotestsum -run TestFunctionName ./...

# Run tests in a specific package
gotestsum ./pkg/mypackage/...

# Watch mode (rerun on file changes)
gotestsum --watch ./...

Test Output Formats

# Default format (clean, colorized)
gotestsum ./...

# Show only test names
gotestsum --format testname ./...

# Dots format (. for pass, F for fail)
gotestsum --format dots ./...

# Group by package
gotestsum --format pkgname ./...

# Standard go test format (with colors)
gotestsum --format standard ./...

# TestDox format (BDD-style output)
gotestsum --format testdox ./...

Common Test Options

# Run with race detection
gotestsum -race ./...

# Generate coverage
gotestsum -cover ./...
gotestsum -coverprofile=coverage.out ./...

# Verbose output
gotestsum -v ./...

# Short mode (skip long-running tests)
gotestsum -short ./...

# Fail fast (stop on first failure)
gotestsum --fail-fast ./...

# Run tests multiple times
gotestsum --count=10 ./...

# Parallel execution
gotestsum -p 4 ./...

# Timeout
gotestsum -timeout 30s ./...

Watch Mode for TDD

# Watch and rerun tests on file changes
gotestsum --watch ./...

# Watch specific package
gotestsum --watch ./pkg/mypackage/...

# Watch with specific format
gotestsum --watch --format testdox ./...

Fallback to go test

If gotestsum is not available, use go test:

# Basic test run
go test ./...

# Verbose
go test -v ./...

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

Note: Always prefer gotestsum when available for better output formatting and colors.

Development Workflow

Standard Go Commands

# Build the project
go build ./...

# Check compilation without building
go check ./...

# Run the application
go run ./cmd/myapp

# Install binary
go install ./cmd/myapp

# Format code
go fmt ./...
gofmt -w .

# Vet code for issues
go vet ./...

Module Management

# Initialize module
go mod init github.com/user/project

# Add dependencies
go get github.com/some/[email protected]

# Update dependencies
go get -u ./...

# Tidy dependencies (remove unused)
go mod tidy

# Vendor dependencies
go mod vendor

# Verify dependencies
go mod verify

# Download dependencies
go mod download

Building

# Build current package
go build

# Build with output path
go build -o bin/myapp ./cmd/myapp

# Build all packages
go build ./...

# Cross-compile
GOOS=linux GOARCH=amd64 go build -o bin/myapp-linux ./cmd/myapp

# Build with version info
go build -ldflags "-X main.version=1.2.3" ./cmd/myapp

# Static binary (no CGO)
CGO_ENABLED=0 go build -o bin/myapp ./cmd/myapp

Code Quality

# Format code
go fmt ./...

# Vet for issues
go vet ./...

# Run staticcheck (if installed)
staticcheck ./...

# Run golangci-lint (if installed)
golangci-lint run

# Check imports
goimports -w .

Testing Best Practices

Test File Organization

// mypackage_test.go
package mypackage_test  // External tests (test public API)

// Or
package mypackage       // Internal tests (test private functions)

Writing Tests

// Table-driven tests (PREFERRED)
func TestMyFunction(t *testing.T) {
    tests := []struct {
        name    string
        input   string
        want    string
        wantErr bool
    }{
        {
            name:  "valid input",
            input: "hello",
            want:  "HELLO",
        },
        {
            name:    "empty input",
            input:   "",
            wantErr: true,
        },
    }

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

Test Helpers

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

// Use t.Cleanup() for teardown
func TestWithCleanup(t *testing.T) {
    tmpDir := setupTempDir(t)
    t.Cleanup(func() {
        os.RemoveAll(tmpDir)
    })
    // test code
}

Benchmarks

# Run benchmarks
gotestsum -bench=. ./...

# Or with go test
go test -bench=. ./...

# Benchmark with memory allocation stats
go test -bench=. -benchmem ./...

# Run specific benchmark
go test -bench=BenchmarkMyFunction ./...

Common Workflows

TDD Workflow

# 1. Start watch mode
gotestsum --watch --format testdox ./...

# 2. Write failing test
# 3. Write code to make test pass
# 4. Refactor
# 5. Repeat

Pre-commit Checks

# Format, vet, and test
go fmt ./... && go vet ./... && gotestsum ./...

# With race detection and coverage
go fmt ./... && go vet ./... && gotestsum -race -cover ./...

Coverage Analysis

# Generate coverage report
gotestsum -coverprofile=coverage.out ./...

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

# Show coverage per function
go tool cover -func=coverage.out

# Check coverage percentage
go tool cover -func=coverage.out | grep total

Debugging Tests

# Run specific test with verbose output
gotestsum -v -run TestSpecificFunction ./...

# Run tests with print debugging
gotestsum -v ./... 2>&1 | grep "DEBUG"

# Use delve for debugging
dlv test ./pkg/mypackage -- -test.run TestSpecificFunction

Environment Variables

# Disable CGO
export CGO_ENABLED=0

# Set GOOS/GOARCH for cross-compilation
export GOOS=linux
export GOARCH=amd64

# Set Go module proxy
export GOPROXY=https://proxy.golang.org,direct

# Private modules
export GOPRIVATE=github.com/myorg/*

# Module download mode
export GOMODCACHE=$HOME/go/pkg/mod

gotestsum Advanced Features

Custom Test Commands

# Run tests with custom go test flags
gotestsum -- -tags integration ./...

# Run with build constraints
gotestsum -- -tags "integration e2e" ./...

# JSON output for parsing
gotestsum --jsonfile=test-results.json ./...

# JUnit XML output (for CI)
gotestsum --junitfile=junit.xml ./...

Rerun Failed Tests

# Run tests and save failures
gotestsum --rerun-fails ./...

# Rerun only failed tests from previous run
gotestsum --rerun-fails=2 ./...

Post-run Commands

# Run command after tests
gotestsum --post-run-command='notify-send "Tests done"' ./...

# Multiple commands
gotestsum --post-run-command='echo "Tests complete" && ./deploy.sh' ./...

Quick Reference

# Test with gotestsum (PREFERRED)
gotestsum ./...
gt ./...                    # If alias configured

# Watch mode for TDD
gotestsum --watch ./...

# Race detection
gotestsum -race ./...

# Coverage
gotestsum -cover ./...

# Verbose output
gotestsum -v ./...

# Specific test
gotestsum -run TestName ./...

# Fail fast
gotestsum --fail-fast ./...

# Format code
go fmt ./...

# Vet code
go vet ./...

# Build
go build ./...

# Run
go run ./cmd/myapp

# Module tidy
go mod tidy

Best Practices

1. Use gotestsum for all testing - Better output, colors, and features
2. Write table-driven tests - More maintainable and comprehensive
3. Use t.Helper() for test utilities - Clearer test failure locations
4. Run tests with -race - Catch race conditions early
5. Check coverage - Aim for high test coverage
6. Use go fmt - Consistent code formatting
7. Run go vet - Catch common mistakes
8. Keep tests fast - Use -short flag for quick feedback loops
9. Use subtests with t.Run() - Better organization and parallel execution
10. Clean up with t.Cleanup() - Proper resource management

CI/CD Integration

# Typical CI test command
gotestsum --format pkgname --junitfile junit.xml -- -race -cover -coverprofile=coverage.out ./...

# Generate coverage report
go tool cover -html=coverage.out -o coverage.html

# Check coverage threshold
go tool cover -func=coverage.out | awk '/total:/ {if ($3+0 < 80.0) exit 1}'