I have done some diving and git bisecting into this. There are at least two issues:

1. `Clinic.__init__` no longer works without passing in a filename. Because soon after `if filename` in line 1726 [1] it calls `d('file')` which only works if there is a `file` buffer.
This makes the odd line 38 [2] in clinic_test.py to fail miserably with sys.exit. Deleting this line results in a proper test failure (22 test fail out of 54), which is already much better than the sys exit message.

2. `Clinic` has shifted from using `field_destinations` to `destination_buffers` in issue 23500. The test code did not change accordingly.


This means that we need to adapt the test code to the use `destination_buffers`, and add it to the regular test suite. The whole situation could only have happened because the test were not run regularly.

I would like to tackle this, but I am not entirely sure yet what should the differences between FakeClinic and Clinic be. So I am studying it. Hints are welcome.




[1] https://github.com/python/cpython/blob/6969eaf4682beb01bc95eeb14f5ce6c01312e297/Tools/clinic/clinic.py#L1726

[2] https://github.com/python/cpython/blob/6969eaf4682beb01bc95eeb14f5ce6c01312e297/Tools/clinic/clinic_test.py#L38