On macOS, there are two test failure seen with test_sidebar (tested on 10.14 with Tk 8.6.8 and 8.6.0 - the failures should be reproducible with the python.org 3.8.0b3 installer for macOS which will be available soon.)

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FAIL: test_click_selection (idlelib.idle_test.test_sidebar.LineNumbersTest)
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Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/idle_test/test_sidebar.py", line 253, in test_click_selection
    self.assertEqual(self.get_selection(), ('2.0', '3.0'))
AssertionError: Tuples differ: ('1.0', '2.0') != ('2.0', '3.0')

First differing element 0:
'1.0'
'2.0'

- ('1.0', '2.0')
+ ('2.0', '3.0')

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FAIL: test_drag_selection (idlelib.idle_test.test_sidebar.LineNumbersTest)
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Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/idlelib/idle_test/test_sidebar.py", line 273, in test_drag_selection
    self.assertEqual(self.get_selection(), ('1.0', '4.0'))
AssertionError: Tuples differ: ('1.0', '3.0') != ('1.0', '4.0')

First differing element 1:
'3.0'
'4.0'

- ('1.0', '3.0')
?          ^

+ ('1.0', '4.0')
?          ^


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