;

      test_interpolation({
        property: 'grid-template-columns',
        from: "1fr [a b] 1fr [d] 1fr",
        to: "2fr [c] auto 2fr"
      }, [
        {at: -1, expect: "0fr [a b] 1fr [d] 0fr"},
        {at: 0, expect: "1fr [a b] 1fr [d] 1fr"},
        {at: 0.4, expect: "1.4fr [a b] 1fr [d] 1.4fr"},
        {at: 0.6, expect: "1.6fr [c] auto 1.6fr"},
        {at: 1, expect: "2fr [c] auto 2fr"},
        {at: 2, expect: "3fr [c] auto 3fr"}
      ]);

      test_interpolation({
        property: 'grid