[56steve]

MockClock accepted a NaN rate because the check was new_rate < 0, which is false for NaN, so MockClock(rate=float('nan')).current_time() returned nan. I changed the check so NaN raises the same ValueError as a negative rate, and added tests for both the constructor and the setter.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00000%. Comparing base (354708e) to head (f1c7da7).

Additional details and impacted files

@@               Coverage Diff               @@
##                 main        #3562   +/-   ##
===============================================
  Coverage   100.00000%   100.00000%           
===============================================
  Files             128          128           
  Lines           19479        19484    +5     
  Branches         1323         1323           
===============================================
+ Hits            19479        19484    +5     

Files with missing lines	Coverage Δ
src/trio/_core/_mock_clock.py	100.00000% <100.00000%> (ø)
src/trio/_core/_tests/test_mock_clock.py	100.00000% <100.00000%> (ø)

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[A5rocks]

Please don't respond with LLM-generated comments or I will close this PR!

[A5rocks]

Please make this explicit. math.isnan exists, we don't have to do stupid transformations on math to check for NaN! Also a better error message is possible.