[issue18054] Add more exception related assertions to unittest

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I'm sure not all user of the TestCase class even know about all it's existing methods.

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nosy: +serhiy.storchaka

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18054>
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