Clean Up Testing of Excel Engine Option Setting for Readers/Writers

[WillAyd]

Follow up to this #25092 (comment)

Right now for readers we test directly setting engine= as a keyword argument, whereas in the writer tests we set the global option. I think we should consistently set the keyword argument and simply have a test on both reading / writing that setting the option will actually trigger that keyword argument to improve coverage and keep things simple

[jbrockmendel]

Has this been addressed? IIRC we did quite some refactoring of excel tests in late 2019

[WillAyd]

It's open ended - let's close for now can come back if there's something concretely actionable