Inconsistent behavior of the `desc` argument in `testthat::test_file(desc=...)`

[kubajal]

There are 2 consistency issues with test_file(desc=...):

• you can't select a nested describe expression (and their nesting is allowed as per https://testthat.r-lib.org/reference/describe.html)
• you can't select a single it statement for execution (analogously to how you are able to select a single test_that or describe expression)

Implementing more granular selection of tests that the user wants to run would improve the UX of testthat. Additionally, better IDE integrations would be possible (e.g. fixing an old issue in meakbiyik/vscode-r-test-adapter#24 which I'm working on).

I have partially implemented the more granular way to run the tests in #2077 but it was rejected. Moreover, I'm aware now of 1 bug in my code which I want to fix. I can't however reopen that PR.

I'll appreciate any input on that topic from the maintainers side. I'm ready to properly implement it.

[hadley]

Fixed by #2077