[issue18937] add unittest assertion for logging

[Michael Foord]

Michael Foord added the comment:

The patch and approach look good to me (with docs needed).

Note, personally I would not use a leading underscore for the assertion methods (in the tests) _assertNoStderr and _assertLogRecords.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18937>
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