Add a `deselected` parameter to `assert_outcomes()`

[okken]

What's the problem this feature will solve?

I'd like to be able to use pytester.RunResult.assert_outcomes() to check deselected count.

Describe the solution you'd like

Add a deselected parameter to pytester.RunResult.assert_outcomes()

Plugins that use pytest_collection_modifyitems to change the items and add change the deselected items need to be tested. Using assert_outcomes() to check the deselected count would be helpful.

Alternative Solutions

Use parseoutcomes() instead of assert_outcomes(). parseoutcomes() returns a dictionary that includes deselected, if there are any.
However, if we have a series of tests, some that care about deselected, and some that don't, then we may have some tests using assert_outcomes() and some using parseoutcomes(), which is slightly annoying.

Additional context

[nicoddemus]

Sounds reasonable. 👍

[devanshikhatsuriya]

Hi! I would like to work on this proposal. I went ahead and modified pytester.RunResult.assert_outcomes() to also compare the deselected count to that returned by parseoutcomes(). I also modified pytester_assertions.assert_outcomes() called by pytester.RunResult.assert_outcomes().

While all tests pass after the above changes, I think none of the tests presently would be using assert_outcomes() with deselected as a parameter since it's a new feature, so should I also write a test for the same? Can you suggest how I should go about doing the same? I am a bit confused as there are many test_ files.

I am new here, so any help/feedback will be highly appreciated. Thanks!

[okken]

Looking at the pull request 8952 would be a good place to start.
That PR involved adding warnings to assert_outcomes(), so it will also show you where all you need to make sure to have changes.
It also includes a test.
The test for deselected will have to be different.
Using -k or -m will be effective in creating deselected tests.
One option is to have two tests, test_one and test_two, for example, and call pytester.runpytest("-k", "two").
That should produce one passed and one deselected.

[okken]

One exception to the necessary changes. I don't think test_nose.py mods would be necessary. Of course, I'd double check with @nicoddemus.

[okken]

didn't mean to close