We have quite a number of tests that specify keys, such as sound and printer.
But when the test is run I don't know of any way to tell if the tests are being run because that keyword was a filter, or if they being run because there was no filter on the jtreg command line.
If a test can tell, it has additional flexibility in deciding whether it is appropriate to "skip".
For example, a test may choose to skip if there's no printer.
But if it can tell that it was explicitly selected because of the printer keyword, then it might choose to fail in such a case, as it really should then run.

So for this feature to apply
- the test must have an @key
- the jtreg command line must specify that this key is required (I don't think "!" cases are relevant)

The manifestation could be a system property like "test.src" but in this case "test.keywords" - probably plural since in theory a test could have
@key printer sound

and the filter could be "-k sound & printer"

but I've not thought through all those details.