Tests for AnimationNode methods

Tests for AnimationNode methods
Please test node3, node4, node3 to ensure that the specification is correctly captured:
'To insert ... perform the following steps for each node in nodes:
  1. Remove node from its parent.
  2. Insert node to parent's list of child animation nodes before reference child.'

The expected behaviour would be:
a. node3 inserted before node2 (-> node1, node3, node2)
b. node4 inserted before node2 (-> node1, node3, node4, node2)
c. node3 inserted before node2 (-> node1, node4, node3, node2)