[Django] #37076: assertWarnsMessage() only checks the first warning for a matching message

[Django]

#37076: assertWarnsMessage() only checks the first warning for a matching message
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Reporter: Mike Edmunds | Type: Bug
Status: new | Component: Testing
| framework
Version: 6.0 | Severity: Normal
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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`assertWarnsMessage(category, message)` fails if the ''first'' warning
issued in `category` does not contain `message`, even if some later
warning does match.

As a result, test cases depend on the specific order warnings are issued.
This can become confusing when there are several related deprecations
going in at once, or when a feature being tested uses some other feature
that also issues a warning.

For example, you might expect this test to pass, but it fails with
`AssertionError: 'Deprecated in MyApp' not found in 'Deprecated in
Django'`:

{{{#!python
class MyAppTests(SimpleTestCase):
def test_deprecated_in_my_app(self):
with self.assertWarnsMessage(DeprecationWarning, "Deprecated in
MyApp"):
# MyApp calls something in Django that happens to be
deprecated:
warnings.warn("Deprecated in Django",
RemovedInNextVersionWarning)
# Then MyApp issues the warning being tested:
warnings.warn("Deprecated in MyApp", DeprecationWarning)
}}}

If you switch the order of the two warnings, the test passes. (And the
second warning is then ignored—see #37072.)

There is a workaround by combining a very carefully crafted
`ignore_warnings()` context with `assertWarnsMessage()`. (It requires
knowing that the semi-documented `ignore_warnings()` also accepts a
`message` argument. And that it interprets it quite differently from
`assertWarnsMessage()`.)
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Ticket URL: <https://code.djangoproject.com/ticket/37076>
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