4.3. Can I have more than one TEST.ROOT?

In general, no. Each test is uniquely associated with exactly one test root directory, which is the the smallest enclosing directory containing a marker file called TEST.ROOT. In general, a test run will consist of tests from a single test suite, identified by a single test root directory.

It is possible to run tests from multiple test suites (such as jdk/test and langtools/test) but this is not common.