macOS test failed twice for PR-18536, for reasons unrelated to the IDLE test additions.  Two pages gave completely different reasons.

https://github.com/python/cpython/pull/18536/checks?check_run_id=451798955

clang: warning: -framework Tk: 'linker' input unused [-Wunused-command-line-argument]
In file included from /Users/runner/runners/2.164.0/work/cpython/cpython/Modules/_tkinter.c:48:
/Applications/Xcode_11.3.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/tk.h:86:11: fatal error: 'X11/Xlib.h' file not found
#       include <X11/Xlib.h>
                ^~~~~~~~~~~~
1 error generated.

Python build finished successfully!

But no tests are listed.

From clicking '...' on above page, View raw logs,
https://pipelines.actions.githubusercontent.com/E9sxbx8BNoRYbzXilV3t7ZRT2AjSeiVsTIIDUiDv0jTXfwuZPt/_apis/pipelines/1/runs/4122/signedlogcontent/6?urlExpires=2020-02-18T02%3A39%3A17.4773408Z&urlSigningMethod=HMACV1&urlSignature=ZpdM7bjMgqeUyUCyD4TLVZRYpMxqvYw%2BA9bEs0qCKfE%3D

2020-02-18T02:24:55.9857810Z ======================================================================
2020-02-18T02:24:55.9858110Z FAIL: test_case_insensitivity (test.test_importlib.extension.test_case_sensitivity.Source_ExtensionModuleCaseSensitivityTest)
2020-02-18T02:24:55.9858780Z ----------------------------------------------------------------------
2020-02-18T02:24:55.9858930Z Traceback (most recent call last):
2020-02-18T02:24:55.9859090Z   File "/Users/runner/runners/2.164.0/work/cpython/cpython/Lib/test/test_importlib/extension/test_case_sensitivity.py", line 36, in test_case_insensitivity
2020-02-18T02:24:55.9859680Z     self.assertTrue(hasattr(loader, 'load_module'))
2020-02-18T02:24:55.9859810Z AssertionError: False is not true

This happened with 2 subtests.
  
======================================================================
2020-02-18T02:24:55.9860160Z FAIL: test_insensitive (test.test_importlib.source.test_case_sensitivity.Frozen_CaseSensitivityTestPEP302)
2020-02-18T02:24:55.9860780Z ----------------------------------------------------------------------
2020-02-18T02:24:55.9860940Z Traceback (most recent call last):
2020-02-18T02:24:55.9861090Z   File "/Users/runner/runners/2.164.0/work/cpython/cpython/Lib/test/test_importlib/source/test_case_sensitivity.py", line 57, in test_insensitive
2020-02-18T02:24:55.9861400Z     self.assertIsNotNone(insensitive)
2020-02-18T02:24:55.9861530Z AssertionError: unexpectedly None

4 subtests failed.