Add tests for transitions

[silviot]

These tests rely on the existing object definitions.

The following transition, defined in the test, should probably be added to the existing ones.

('last', 2, 3): {
                'actor_end': 5,
                'actor_start': 2,
                'last_use': False,
                'modify_uses': [0, 0],
                'target_end': 3,
                'target_start': 3,
                'visible': 'always'
            },