Track names used within a single test file

[schloerke]

Since we are wrapping testthat::test_dir(), we can wrap testthat::test_dir(reporter=) which has access to reporter$start_file(file) / $end_file(file).

Idea:

• Wrap this reporter with a {shinytest2} shim to capture the file value.
• When saving a snapshot file, check for the known names that have been seen if the reporter flag is set.
• Ignore if the flag is not set

Possible problems:

• Executing tests in parallel

[schloerke]

Marking this issue as wontfix as there is no good fix but to fix it upstream in {testthat}

[schloerke]

Fixed in r-lib/testthat#1592