t.Setenv is the modern standard Go testing utility (since Go 1.17) that automatically restores environment variables when the test completes. This replaces the custom testutil.WithEnvVar function which manually saved and restored env var state.
The testutil.go file is deleted as it only contained WithEnvVar. The testutil package remains for its other utilities like KubeconfigBuilder.
Modernize the codebase to use idiomatic Go 1.25 patterns, removing deprecated APIs and reducing external dependencies.
- Replace deprecated `io/ioutil` with `os.ReadFile`, `os.WriteFile`, `os.MkdirTemp`, `os.CreateTemp`
- Replace `interface{}` with `any` (Go 1.18+)
- Remove `github.com/pkg/errors` dependency entirely, using stdlib `fmt.Errorf` with `%w` and `errors.New`
- Use `errors.As()` instead of direct type assertions on error values
- Use `strings.Cut()` for delimiter parsing instead of `strings.Split` + length check
- Use `slices.Contains()` for linear search in `ContextExists()`
- Use `t.Setenv()` and `t.TempDir()` in tests instead of manual env save/restore and temp dir cleanup
- Delete unused `internal/testutil/tempfile.go` helper
- Update GitHub Actions CI and release workflows from Go 1.22 to 1.25
Net result: -70 lines, 1 fewer external dependency.
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
