Do not use `ZeroDivisionError` in tests for unrelated things

[sobolevn]

Feature or enhancement

Refs #119066

I'm a little horrified at how often we use ZeroDivisionError in random tests that have nothing to do with arithmetic, but that's another story ...

Probably, most of them should be converted to some custom exception.

[terryjreedy]

Specifically, #119066 (review).
@mdickinson What are examples of horror-inducing uses?

[serhiy-storchaka]

1/0 is just the simplest way to raise a rare exception. We can use raise OtherRareException or even raise CustomError, but this is more verbose.

[terryjreedy]

To answer my question: I routinely use something like a a to get a SyntaxError and specifically 1/0' for a 'generic' runtime error. That said, greppping Lib/test recursively for ZeroDivisionError` gets 524 hits. Some test classes raise the long name itself. For instance:

# test_iter, 83-5.
class BadIterableClass:
 def __iter__(self):
 raise ZeroDivisionError

Others do not:

# test_xml_etree, 2790-2.
class BadElementPath(str):
 def __eq__(self, o):
 raise 1/0

Regardless, the multiple tests using 'Bad' classs require the long error name. I could be persuaded that defining something like class FakeErr, raising that in the Bad class, and checking for the short name in tests would be clearer, as well as involving less writing and reading.

This strikes me as a test style proposal that is plausible but needs discussion on Discord or Discourse before possibly revising PEP8 or Devguide.

Serhiy, only a few in test_tkinter:

test_tkinter\test_colorchooser.py: 49: raise ZeroDivisionError
test_tkinter\test_colorchooser.py: 53: self.assertRaises(ZeroDivisionError, askcolor)
test_tkinter\test_colorchooser.py: 59: self.assertRaises(ZeroDivisionError, askcolor)
test_tkinter\test_messagebox.py: 18: raise ZeroDivisionError
test_tkinter\test_messagebox.py: 22: self.assertRaises(ZeroDivisionError, showinfo, "Spam", "Egg Information")
test_tkinter\test_messagebox.py: 27: self.assertRaises(ZeroDivisionError, showinfo, "Spam", "Egg Information")

[mdickinson]

@terryjreedy @sobolevn I apologise for causing unnecessary work and brain cycles here; I think I shouldn't have made the original comment, and definitely shouldn't have used the word "horrified".

I do think that this is a (very minor) abuse of ZeroDivisionError, but my complaint is very much at nitpick level. That is, if I were reviewing a PR that used raise ZeroDivisionError I might suggest introducing and using a custom exception, but I don't think it's worth changing existing cases of this. We have better ways to spend core developer cycles.