golang-testing

Go Testing Patterns

Use the project's installed version and conventions. Verify version-sensitive APIs, security settings, and deployment support with documentation-lookup before applying examples; these patterns are reference guidance, not a tested guarantee for every current release. Do not replace an existing toolchain solely to match an example.

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

Step-by-Step TDD in Go

// Step 1: Define the interface/signature
// calculator.go
package calculator

func Add(a, b int) int {
    panic("not implemented") // Placeholder
}

// Step 2: Write failing test (RED)
// calculator_test.go
package calculator

import "testing"

func TestAdd(t *testing.T) {
    got := Add(2, 3)
    want := 5
    if got != want {
        t.Errorf("Add(2, 3) = %d; want %d", got, want)
    }
}

// Step 3: Run test - verify FAIL
// $ go test
// --- FAIL: TestAdd (0.00s)
// panic: not implemented

// Step 4: Implement minimal code (GREEN)
func Add(a, b int) int {
    return a + b
}

// Step 5: Run test - verify PASS
// $ go test
// PASS

// Step 6: Refactor if needed, verify tests still pass

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)
            }
        })
    }
}