t.Errorf("Failed to unmarshal input %q: %v", c.input, err)
		}
		if result.D != c.result {
			t.Errorf("Failed to unmarshal input %q: expected %q, got %q", c.input, c.result, result)
		}
	}
}

func TestDurationMarshalJSON(t *testing.T) {
	cases := []struct {
		input  Duration
		result string
	}{
		{Duration{5 * time.Second}, `{"d":"5s"}`},
		{Duration{2 * time.Minute}, `{"d":"2m0s"}`},