pytest-xdist support, test stability

[tony]

Changes

Add pytest-xdist dev package

See also:

• https://pypi.org/project/pytest-xdist/
• https://github.com/pytest-dev/pytest-xdist

Flakey tests

• retry_until() tests: Relax clock in assert (pytest-xdist support, test stability #522).
• tests/test_pane.py::test_capture_pane_start: Use retry_until() to poll, improve correctness of test (pytest-xdist support, test stability #522).

See also

• pytest-xdist issues when libtmux > v0.16.1 #468
• Prevent accidental use of incompatible libtmux ansible/ansible-navigator#1685
• Update libtmux ansible/ansible-navigator#1663

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.62%. Comparing base (262127f) to head (5138853).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #522      +/-   ##
==========================================
- Coverage   88.71%   88.62%   -0.09%     
==========================================
  Files          37       36       -1     
  Lines        3960     3922      -38     
  Branches      573      570       -3     
==========================================
- Hits         3513     3476      -37     
+ Misses        306      304       -2     
- Partials      141      142       +1     

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