Tests updated / expanded

Now checking whether size actually changed
Also checking whether circumference is being re-calculated and is correct size (currently with rather large margin for error due to Catroid <-> Box2D conversion inaccuracies)
Testing setting size to larger, smaller, same and zero scale/size
It is maybe better if you use assertEquals(...) instead of assertTrue (all three times)
http://junit.sourceforge.net/javadoc/org/junit/Assert.html#assertEquals(double, double, double)