Would it be possible to add a recursive argument to test_dir() so that it (optionally) also looks for test files in sub-directories?

Motivation:
I have a workflow where I put long running tests - or tests that needs stuff like database access - in subfolders of the /test directory. This works really well as they are not automatically executed by devtools::test(), but I can still manually trigger them. I even made a package to support this worklfow (testthis).

Now if I want to run all tests in a directory and it's subdirectories at once, I have to resort to some really ugly code where i just use with_mock to override the test file discovery of testthat:

  testthat::with_mock(
    devtools::test(...),
    `testthat::find_test_scripts` = find_test_scripts_mock
  )

I'd really love to be able to remove this abomination from my package, especially since with_mock() is deprecated.