The Behaviour class and its implementations have been replaced by the
new animation framework API and by the constraints for layout-related
animations.
Currently, we need to make tests build, so we undef DISABLE_DEPRECATED
in specific test cases while they get ported.
The test was calling g_object_get to fetch the "opacity-start" property
(unsigned int) into a guint8 local variable. It's a bit of a mean trap
given that the getter function returns guint8 values so this also adds a
comment explaining what's going on.
The coverage of the Behaviour sub-classes is currently abysmal. An
initial test suite for Behaviours should at least verify that the
accessors and the constructors are doing the right thing.
This initial test suite just verifies the BehaviourOpacity sub-class,
but it already bumps up the overall coverage by 2%.
