twisted.trial.test.test_assertions.TestCallDeprecated.test_callDeprecatedSuppressesWarning overrides warnings.warn_explicit to catch emitted warnings

[exarkun]

This test tries to assert that no warnings are emitted when callDeprecated is used to call a function which emits a deprecation warning. It replaces warnings.warn_explicit for the duration of the test and expects to be able to observe warnings through its replacement. In Python 2.6, this strategy will not work. The test should likely use the strategy used in the implementation of TestCase.assertWarns (which perhaps should be factored into a general API, at least for internal-trial use).

[exarkun]

(In [24952]) reimplement callDeprecated in terms of flushWarnings; strengthen the assertion about ignored warnings

refs #3427

This likely resolved #3427 since it removes the use of warn_explicit from the mentioned test method.

[exarkun]

(In [25279]) Merge flushwarnings-3487

Author: radix, itamar, exarkun Reviewer: glyph Fixes: #3487 Fixes: #3427 Fixes: #2820 Fixes: #3506

Introduce TestCase.flushWarnings, an API for interacting with the Python warnings module in unit tests. By default, the default trial reporter will write warnings emitted by tests to its output stream (no longer does the runner print them to stdout). flushWarnings may be used to prevent this from happening in particular tests, and its return value may be used to make assertions about what warnings have been emitted. TestCase.assertWarns and TestCase.callDeprecated are both now implemented in terms of this more flexible API.

The default reporter includes rudamentary support for duplicate suppression: each warning will be reported only once per test, but if a warning is emitted by two or more tests, it will be reported for each test (isolating tests from each other further by making warning behavior the same regardless of what other tests have run).

There is also some support for failing tests based on warnings emitted. If the Python warnings filters system is used to turn a warning into an exception, any test which causes such a warning to be emitted will have an error attributed to it.