Test calling getPropertyValue on computed styles for background-position properties.

background-position: 0;
  background-position
    getPropertyValue:    0px 50%
  background-position-x
    getPropertyValue:    0px
  background-position-y
    getPropertyValue:    50%
background-position: 0 0;
  background-position
    getPropertyValue:    0px 0px
  background-position-x
    getPropertyValue:    0px
  background-position-y
    getPropertyValue:    0px

background-position: 15px;
  background-position
    getPropertyValue:    15px 50%
  background-position-x
    getPropertyValue:    15px
  background-position-y
    getPropertyValue:    50%
background-position: 10px 20px;
  background-position
    getPropertyValue:    10px 20px
  background-position-x
    getPropertyValue:    10px
  background-position-y
    getPropertyValue:    20px

No background-position set
  background-position
    getPropertyValue:    0% 0%
  background-position-x
    getPropertyValue:    0%
  background-position-y
    getPropertyValue:    0%