[issue40331] Increase test coverage for the statistics module

[Tzanetos Balitsaris]

Change by Tzanetos Balitsaris <tbalitsaris at gmail.com>:


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keywords: +patch
pull_requests: +18941
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/19608

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40331>
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