The harness can run tests concurrently. If you are running the tests on a multi-processor computer, concurrency can speed up your test runs. The default range of values used by the JT Harness harness is from 1 to 50.

For your first test run you should leave this field set to "1". After you have the tests running properly you can experiment with this value. Unless your test suite restricts concurrency, the maximum number of threads specified by the `concurrency` command is 50. See your test suite documentation for additional information about using concurrency values greater than 1.