Add tests for sprite prototype properties
Add tests for ship and bigAlien sprites
Use sinon.assert.called consistently to check if stubs have been called
Use indexing of filtered array instead of pop, not an important change
Reduce code duplication in tests using new local spriteWithName function
Change name and behaviour of spriteWithName so it can be used to remove even more duplication
Rename grid variable to prevGrid and use new grid variable to reduce length of lines
Stub Ship constructor in rendering and assert that ship is added as attribute of Game
Add test for displayScore function, + stubbing
Add tests for drawExtraLives, including improved stubbing