Have you tried calling multiline_output() in the REPL?

It does *not* show your expected output:

    # expected
    First line
    Second line


but the string repr():

    # actual
    'First line\nSecond line\n'



Change your doctest to either:


    >>> multiline_output()
    'First line\\nSecond line\\n'

(note that you must escape the backslashes) or:

    >>> print(multiline_output())
    First line
    Second line
    <BLANKLINE>


Note that the "<BLANKLINE>" needs to be written literally, as described here:

https://docs.python.org/3/library/doctest.html#doctest.DONT_ACCEPT_BLANKLINE