golang-testing

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• SKILL.md

SKILL.md (first lines)

# 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
```

### Step-by-Step TDD in Go

```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.

```go
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)
            }
        })
    }
}
```

### Table-Driven Tests with Error Cases

```go
func TestParseConfig(t *testing.T) {
    tests := []struct {
        name    string
        input   string
        want    *Config
        wantErr bool
    }{
        {
            name:  "valid config",
            input: `{"host": "localhost", "port": 8080}`,
            want:  &Config{Host: "localhost", Port: 8080},
        },
        {
            name:    "invalid JSON",
            input:   `{invalid}`,
            wantErr: true,
        },
        {
            name:    "empty input",
            input:   "",
            wantErr: true,

From ViewWay/hermes-by-everythings, MIT.

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