    test_interpolation({
        property: 'grid-template-columns',
        from: "1fr repeat(2, 2fr auto 30px) 1fr",
        to: "2fr repeat(2, 3fr 30px 40px) 2fr"
      }, [
        {at: -1, expect: "0fr repeat(2, 1fr auto 20px) 0fr"},
        {at: 0, expect: "1fr repeat(2, 2fr auto 30px) 1fr"},
        {at: 0.4, expect: "1.4fr repeat(2, 2.4fr auto 34px) 1.4fr"},
        {at: 0.6, expect: "1.6fr repeat(2, 2.6fr 30px 36px) 1.6fr"},
        {at: 1, expect: "2fr repeat(2, 3fr 30px 40px) 2fr"},
        {at: 2