Python function ending with 'return """' produces "All tests passed!"

[x77686d]

It appears that a Python solution ending with 'return """' (triple double-quote) produces "All tests passed!" even though it's a syntax error. Sample code:

def grid_is_square(x):
        return """

Here's what the student sees:

The progress summary shows the following. Note the gray bar (not started(?)) and green bar (passed) for grid_is_square.