Testery enables you to set the number of parallel tests to optimize how your test runs are queued up or throttle test runs so they don't overwhelm the system-under-test.
Setting Number of Parallel Tests for a Scheduled Test Run
When editing the scheduled test run, select Show Advanced Options and specify the Number of Parallel tests. Be sure to set this number to less than the total available for your account if you'd like to be able to have multiple test runs running at the same time.
Setting the Number of Parallel Tests for an Ad Hoc Test Run
You can also set the number of parallel tests when running an ad hoc test run. To do this, when creating the test run, expand Show Advanced Options and specify the desired number of parallel tests.