This test tests that discard acts the same as removeChild.
First two red rects and a blue circle should be seen. The blue circle has
its radius animated to 0 over the course of 3 seconds. At the point where
the blue circle disappears the two red rects should be removed from the
tree. This reveals two green circles.
The test has passed if in the interval 0-3 seconds there are two red rects and a blue circle, and after 3 seconds two green circles can be seen and the text at the bottom says "Test passed".
