`test_pickle` tests failing when invoked directly

[donBarbos]

I ran separate tests for the pickle module on main branch:

./python ./Lib/test/test_pickle.py

I got 24 failures
Judging by the output, the problem is in the mismatch of error messages:

test_nested_lookup_error (__main__.CPicklingErrorTests.test_nested_lookup_error) ...
  test_nested_lookup_error (__main__.CPicklingErrorTests.test_nested_lookup_error) (proto=0) ... FAIL
  test_nested_lookup_error (__main__.CPicklingErrorTests.test_nested_lookup_error) (proto=1) ... FAIL
  test_nested_lookup_error (__main__.CPicklingErrorTests.test_nested_lookup_error) (proto=2) ... FAIL
  test_nested_lookup_error (__main__.CPicklingErrorTests.test_nested_lookup_error) (proto=3) ... FAIL
  test_nested_lookup_error (__main__.CPicklingErrorTests.test_nested_lookup_error) (proto=4) ... FAIL
  test_nested_lookup_error (__main__.CPicklingErrorTests.test_nested_lookup_error) (proto=5) ... FAIL
...
test_wrong_object_lookup_error (__main__.CPicklingErrorTests.test_wrong_object_lookup_error) ...
  test_wrong_object_lookup_error (__main__.CPicklingErrorTests.test_wrong_object_lookup_error) (proto=0) ... FAIL
  test_wrong_object_lookup_error (__main__.CPicklingErrorTests.test_wrong_object_lookup_error) (proto=1) ... FAIL
  test_wrong_object_lookup_error (__main__.CPicklingErrorTests.test_wrong_object_lookup_error) (proto=2) ... FAIL
  test_wrong_object_lookup_error (__main__.CPicklingErrorTests.test_wrong_object_lookup_error) (proto=3) ... FAIL
  test_wrong_object_lookup_error (__main__.CPicklingErrorTests.test_wrong_object_lookup_error) (proto=4) ... FAIL
  test_wrong_object_lookup_error (__main__.CPicklingErrorTests.test_wrong_object_lookup_error) (proto=5) ... FAIL
...
test_nested_lookup_error (__main__.PyPicklingErrorTests.test_nested_lookup_error) ...
  test_nested_lookup_error (__main__.PyPicklingErrorTests.test_nested_lookup_error) (proto=0) ... FAIL
  test_nested_lookup_error (__main__.PyPicklingErrorTests.test_nested_lookup_error) (proto=1) ... FAIL
  test_nested_lookup_error (__main__.PyPicklingErrorTests.test_nested_lookup_error) (proto=2) ... FAIL
  test_nested_lookup_error (__main__.PyPicklingErrorTests.test_nested_lookup_error) (proto=3) ... FAIL
  test_nested_lookup_error (__main__.PyPicklingErrorTests.test_nested_lookup_error) (proto=4) ... FAIL
  test_nested_lookup_error (__main__.PyPicklingErrorTests.test_nested_lookup_error) (proto=5) ... FAIL
...
test_wrong_object_lookup_error (__main__.PyPicklingErrorTests.test_wrong_object_lookup_error) ...
  test_wrong_object_lookup_error (__main__.PyPicklingErrorTests.test_wrong_object_lookup_error) (proto=0) ... FAIL
  test_wrong_object_lookup_error (__main__.PyPicklingErrorTests.test_wrong_object_lookup_error) (proto=1) ... FAIL
  test_wrong_object_lookup_error (__main__.PyPicklingErrorTests.test_wrong_object_lookup_error) (proto=2) ... FAIL
  test_wrong_object_lookup_error (__main__.PyPicklingErrorTests.test_wrong_object_lookup_error) (proto=3) ... FAIL
  test_wrong_object_lookup_error (__main__.PyPicklingErrorTests.test_wrong_object_lookup_error) (proto=4) ... FAIL
  test_wrong_object_lookup_error (__main__.PyPicklingErrorTests.test_wrong_object_lookup_error) (proto=5) ... FAIL

Examples of mismatches:

AssertionError: "type object 'AbstractPickleTests' has no attribute 'spam'" != "module '__main__' has no attribute 'AbstractPickleTests'"
- type object 'AbstractPickleTests' has no attribute 'spam'
+ module '__main__' has no attribute 'AbstractPickleTests'
...
AssertionError: "Can'[53 chars]4b0>: it's not the same object as __main__.AbstractPickleTests" != "Can'[53 chars]4b0>: it's not found as __main__.AbstractPickleTests"
- Can't pickle <test.pickletester.REX object at 0x79fcb255a4b0>: it's not the same object as __main__.AbstractPickleTests
?                                                                         ^^^^^^^^^ ^^^^^
+ Can't pickle <test.pickletester.REX object at 0x79fcb255a4b0>: it's not found as __main__.AbstractPickleTests
?

I'm going to send PR after we decide what the messages should look like

Linked PRs

• gh-131031: Fix separated running of pickle tests #133218
• gh-131031: Fix test_pickle when invoked directly #133356
• [3.14] gh-131031: Fix test_pickle when invoked directly (GH-133356) #133673
• [3.13] gh-131031: Fix test_pickle when invoked directly (GH-133356) #133675

[serhiy-storchaka]

Good catch @donBarbos! Thank you.

Your PR fixes tests, but I think that it would be better to not use AbstractPickleTests in these tests. For these tests we need an existing global class which does not exist in __main__ . Running tests as a script fails because AbstractPickleTests is imported in test_pickle.py which becomes __main__. #133356 uses this approach.