Helper function for stabilizing slog.Logger output during testing.

helper.go

// NewSlogStabilizer returns a [slog.Handler] ReplaceAttr function that replaces
// non-deterministic attribute values with stable values.
//
// All attribute values of type [time.Time] and [time.Duration] are replaced
// with their zero values.
//
// Usage:
//
//	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
//	 ReplaceAttr: NewSlogStabilizer(t)
//	}))
func NewSlogStabilizer(tb testing.TB) func([]string, slog.Attr) slog.Attr {
	tb.Helper()

	return func(_ []string, a slog.Attr) slog.Attr {
		tb.Helper()

		switch a.Value.Any().(type) {
		case time.Time:
			return slog.Attr{Key: a.Key, Value: slog.TimeValue(time.Time{})}
		case time.Duration:
			return slog.Attr{Key: a.Key, Value: slog.DurationValue(time.Duration(0))}
		default:
			return a
		}
	}
}