def test_clear_does_not_turn_on_pixels(self):
"""Clearing does not activate any pixels that were already off"""
v = VideoRam(20, 20)
v.clear_screen()
for x, y in all_coordinates(v):
assert not v.pixels[y * v.width + x]
def test_clear_turns_off_pixels(self):
"""Pixels turned on are switched off"""
v = VideoRam(21, 21)
for pixel_index in range(len(v.pixels)):
if pixel_index % 2:
v.pixels[pixel_index] = True
v.clear_screen()
for x, y in all_coordinates(v):
assert not v[x, y]