$ ./python -m test -uall test_idle 
Run tests sequentially
0:00:00 load avg: 1.19 [1/1] test_idle
invalid command name "140662890299080timer_event"
    while executing
"140662890299080timer_event"
    ("after" script)
test test_idle failed -- Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/idlelib/idle_test/test_configdialog.py", line 417, in test_highlight_target_text_mouse
    click_it(start_index)
  File "/home/serhiy/py/cpython/Lib/idlelib/idle_test/test_configdialog.py", line 401, in click_it
    x, y, dx, dy = hs.bbox(start)
TypeError: 'NoneType' object is not iterable

test_idle failed

1 test failed:
    test_idle

Total duration: 2 sec
Tests result: FAILURE


Maybe this is related to HiDPI display.

On 2.7 the test is passed.

Are you running on Linux or Mac?  What tk version?

About the 'invalid command name' message: PR3622, patching idlelib.codecontext, merged to master 13 hours ago, fixed this for me on Windows.  (It added CodeContext.__del__.)  Did it fail on your machine or was it not yet merged on your machine?

About the test failure.  Hs is a Text with about 14 lines.  The test initially executes
        hs.see(1.0)
        hs.update_idletasks()
hs.bbox(start) means that the tag start is not visible,  which should realistically not be possible.  But a quick web search suggests there have been problems with HiDPI and tk, and hence tkinter.

I am curious what value of start fails.  Could you run once with 'print(start)' added above bbox(start)?

Does inserting the following just before hs.bbox(start) fix the issue?
        hs.see(start)
        hs.update_idletasks()
If not, we can skip.  Does the following print one or multiple skip messages?
        try:
            x, y, dx, dy = hs.bbox(start)
        except TypeError:
            self.skipTest(f'bbox failure with start {start}')

About the 'invalid command name' message: PR 3622 was not yet merged on your machine.

Inserting hs.see(start) just before hs.bbox(start) fixes the issue.

I have added some debug prints. Here are outputs, with and without a fix.

On windows, hs.see(start), followed or not by update_idletasks(), has no effect.

Does the fix for #31500 fix this also?

No, the fix for issue31500 doesn't affect this issue.

If the test only fails with a HiDPI screen, then it must somehow be related.  But if the highlight sample is normal size, like the font sample in
https://bugs.python.org/file47141/Screenshot_20170917_213616.png
then the relationship must not be as simple as I was thinking.

Updated patch for issue31500 fixes this issue. I guess the problem was with using fixed size for the dialog widget. It was too small and the part of the example was not visible.