[issue31649] IDLE: Make _htest, _utest parameters keyword-only.

[Terry J. Reedy]

New submission from Terry J. Reedy <tjreedy at udel.edu>:

All calls in tests should pass as keyword.  Get better error message if pass wrong number of other arguments positionally.

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue31649>
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