go-testing-code-review

# Go Testing Code Review

## Quick Reference

| Issue Type | Reference |
|------------|-----------|
| Test structure, naming | [references/structure.md](references/structure.md) |
| Mocking, interfaces | [references/mocking.md](references/mocking.md) |

## Review Checklist

- [ ] Tests are table-driven with clear case names
- [ ] Subtests use t.Run for parallel execution
- [ ] Test names describe behavior, not implementation
- [ ] Errors include got/want with descriptive message
- [ ] Cleanup registered with t.Cleanup
- [ ] Parallel tests don't share mutable state
- [ ] Mocks use interfaces defined in test file
- [ ] Coverage includes edge cases and error paths

## Critical Patterns

### Table-Driven Tests

```go
// BAD - repetitive
func TestAdd(t *testing.T) {
    if Add(1, 2) != 3 {
        t.Error("wrong")
    }
    if Add(0, 0) != 0 {
        t.Error("wrong")
    }
}

// GOOD
func TestAdd(t *testing.T) {
    tests := []struct {
        name     string
        a, b     int
        want     int
    }{
        {"positive numbers", 1, 2, 3},
        {"zeros", 0, 0, 0},
        {"negative", -1, 1, 0},
    }

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

### Error Messages

```go
// BAD
if got != want {
    t.Error("wrong result")
}

// GOOD
if got != want {
    t.Errorf("GetUser(%d) = %v, want %v", id, got, want)
}

// For complex types
if diff := cmp.Diff(want, got); diff != "" {
    t.Errorf("GetUser() mismatch (-want +got):\n%s", diff)
}
```

### Parallel Tests

```go
func TestFoo(t *testing.T) {
    tests := []struct{...}

    for _, tt := range tests {
        tt := tt  // capture (not needed Go 1.22+)
        t.Run(tt.name, func(t *testing.T) {
            t.Parallel()
            // test code
        })
    }
}
```

### Cleanup

```go
// BAD - manual