pytest.raises has two parameters, message and match. message is meant
to be the error message that pytest gives when the tested code does not
raise the expected exception. match is the string that pytest expects
to be a match for the repr of the exception. Unfortunately, it seems
that message is often mistakenly used where match is meant. Fix those
cases.
message is also deprecated so removed our usage of it. Perhaps we
should write a sanity test later that prevents the use of
pytest.raises(message) to avoid this mistake.
seealso: https://docs.pytest.org/en/4.6-maintenance/deprecations.html#message-parameter-of-pytest-raises
Also update the exception message tested for as we're now properly
detecting that the messages have changed.
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