The existing tests were parameterized to contain the cases both where
the branding form is successfully submitted and those where it isn't. We
were using `pytest.mark.xfail` to check that the tests fail as expected
if there were errors on the form. However, since I'll be changing how
the form validation works, I want to make sure that these tests were
actually failing because of the form validation and not because of
another reason, such as a slight difference in Zendesk ticket output.
This creates separate tests for cases where data entered in the form
is invalid.
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