bpo-36144: Fixed test in test_collections.py

[curtisbucher]

We should be using .copy() to compare key, value pairs and ChainMap in line 257. Otherwise it does not properly check union behavior.
@brandtbucher

https://bugs.python.org/issue36144

[brandtbucher]

Nice catch!

[brandtbucher]

Ubuntu failure looks unrelated.

[aeros]

@brandtbucher

Ubuntu failure looks unrelated.

Yeah it's definitely unrelated, since it failed in the "Install Dependencies" stage. I'll close and re-open the PR to restart the CI checks.

(For some reason, GitHub Actions retains the old failing checks on the same commit, but should still prove that the failure was unrelated to the PR).

[aeros]

Thanks for the PR @curtisbucher.

We should be using .copy() to compare key, value pairs and ChainMap in line 257. Otherwise it does not properly check union behavior.

Agreed; if it's the same object, the test doesn't work as intended. After cm3 |= pairs, even the following would pass:

self.assertEqual(cm3.maps, [cm3.maps[0] | dict(), *cm3.maps[1:]])

(which somewhat defeats the purpose of the test)

[bedevere-bot]

@gvanrossum: Please replace # with GH- in the commit message next time. Thanks!