shadow',
  from: '0px 0px 0px 0px black',
  to: '1px 1px 1px 1px black',
}, [
  {at: -0.3, expect: 'rgb(0, 0, 0) -0.3px -0.3px 0px -0.3px'},
  {at: 0, expect: 'rgb(0, 0, 0) 0px 0px 0px 0px'},
  {at: 0.3, expect: 'rgb(0, 0, 0) 0.3px 0.3px 0.3px 0.3px'},
  {at: 0.6, expect: 'rgb(0, 0, 0) 0.6px 0.6px 0.6px 0.6px'},
  {at: 1, expect: 'rgb(0, 0, 0) 1px 1px 1px 1px'},
  {at: 1.5, expect: 'rgb(0, 0, 0) 1.5px 1.5px 1.5px 1.5px'},
]);

// Test with color as first value.
test_interpolation({
  property: 'box-shadow',