not having explicit @build action might lead to sporadic test failures, therefore all tests directly or indirectly depend on test library classes have to have corresponding explicit build actions.

per Jon Gibbons suggestion[1], all such tests can be found by analyzing classes directory of tests. jdeps tool can be used to get the list of classes required for a specific test.

[1] http://mail.openjdk.java.net/pipermail/core-libs-dev/2017-June/048092.html
You might also be able to do run groups of tests (such as all tests that use a given library) and then look for duplicate classes in the compiled classes directory. Such classes will generally be an indication of implicit compilation.

-- Jon