[issue33744] Fix and improve tests for the uu module

[Serhiy Storchaka]

Change by Serhiy Storchaka <storchaka+cpython at gmail.com>:


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keywords: +patch
pull_requests: +6977
stage:  -> patch review

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33744>
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