Take ANY spinning 3D object, silhouette it, and the same result can be achieved. Much much easier with something simple like a cube though.
The animation would have been done in 3D, and would have been made to spin clock wise (if you were looking down on it) given the way her hair is placed.
Psychologically, the way the figure is positioned will push you to you believe its spinning clockwise, anyone saying otherwise on first glance either is getting clockwise and anti-clockwise mixed up, is very logically minded and managed to not see everything that is in the image at once (ie not normal / has a very weak right brain) Or is lying. (didnt like the the idea of being all emotional ect ect)
Its not really a test, as this type of thing automatically stimulates the right brain functions whether you are naturally a righty or Lefty. Hence the large effort needed to make her spin the other way for most ppl.
Its also why looking at it from funny angles ect can help, as it takes away the brain seing a dancer spinning, and just "a blob", abit like looking at messed up faces that are upside down