[issue21916] Create unit tests for turtle textonly

[R. David Murray]

R. David Murray added the comment:

I made some review comments on ways to use test.support and test.subTest to simplify the code and make it even clearer.  Also, I suggest not using Mock unless necessary (see review comments).

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nosy: +r.david.murray

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21916>
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