  {at: 0, expect: '0px'},
  {at: 0.3, expect: '6px'},
  {at: 0.6, expect: '12px'},
  {at: 1, expect: '20px'},
  {at: 1.5, expect: '30px'},
]);

test_interpolation({
  property: 'padding',
  from: '0px',
  to: '10px'
}, [
  {at: -0.3, expect: '0px'}, // CSS padding can't be negative.
  {at: 0, expect: '0px'},
  {at: 0.3, expect: '3px'},
  {at: 0.6, expect: '6px'},
  {at: 1, expect: '10px'},
  {at: 1.5, expect: '15px'}
]);

test_interpolation({
  property: 'padding',
  from: '20px 40px 60px 80px',
  to: '30px