As reported on StackOverflow:
https://stackoverflow.com/questions/57636747/how-to-perform-assert-has-calls-for-a-getitem-call

The following code would output: [call(), call().foo(), call().foo().__getitem__('bar')]

from unittest.mock import MagicMock, call
mm = MagicMock()
mm().foo()['bar']
print(mm.mock_calls)

but trying to use that list with mm.assert_has_calls([call(), call().foo(), call().foo().__getitem__('bar')]) would result in:

TypeError: tuple indices must be integers or slices, not str

If we go ahead with this then we should also support other dunder methods of tuple like __setitem__ and so on.

Agreed. I've submitted a new commit with the call chaining behavior now generalized for all dunder methods by delegating the resolution of all attributes not directly in the _Call object's __dict__ keys to the getattr method.

Correction. I've now done this by delegating the resolution of attributes belonging to the tuple class to _Call.__getattr__ instead. Passed all build tests.

New changeset 72c359912d36705a94fca8b63d80451905a14ae4 by Michael Foord (blhsing) in branch 'master':
bpo-37972: unittest.mock._Call now passes on __getitem__ to the __getattr__ chaining so that call() can be subscriptable (GH-15565)
https://github.com/python/cpython/commit/72c359912d36705a94fca8b63d80451905a14ae4

New changeset db0d8a5b2c803d30d9df436e00b6627ec8e09a13 by Michael Foord (Miss Islington (bot)) in branch '3.8':
bpo-37972: unittest.mock._Call now passes on __getitem__ to the __getattr__ chaining so that call() can be subscriptable (GH-15565) (GH-15965)
https://github.com/python/cpython/commit/db0d8a5b2c803d30d9df436e00b6627ec8e09a13

Closing as fixed since PRs were merged. Thanks Ben.

New changeset db5e86adbce12350c26e7ffc2c6673369971a2dc by Chris Withers in branch 'master':
Get mock coverage back to 100% (GH-18228)
https://github.com/python/cpython/commit/db5e86adbce12350c26e7ffc2c6673369971a2dc