def test_identity():
""" Concatenating a diff with its inversion should be a no-op """
string = "I'm a lumberjack, and I'm okay. I sleep all night and I work all day."
diff = Diff([("lumberjack,", 2, False), ("parrot", 6, True), ("spam", 8, True)])
no_diff = diff.concat(diff.invert())
assert no_diff.apply(string) == string
def test_invert():
""" Test that an inverted diff undoes a change """
string = "No no no, my fish's name is Eric, Eric the fish. He's an halibut."
diff = Diff([("no", 1, False), ("salt", 8, True)])
altstring = diff.apply(string)
assert diff.invert().apply(altstring) == string