For test runs in which the order of test cases must be maintained(Maintain Order = yes), there is always one Active tester. This is the tester whose turn it is to execute its test case(s) in the test run. The Active tester field is located on the detail screen of the test run. If the test run has not yet started then the tester of the top test case in the Test Cases tab will be the active tester. The Active tester field will then be filled with this tester.
During the execution of the test run, based on the statuses of the test cases, it is determined which tester is next in line to execute his or her test in the test run (the active tester). Using the diagram below, the test cases in the test run are run through to determine who is the active tester. This also takes into account whether there are any blocking instances.
When the Blocking for Testing checkbox is checked in a defect and the status of the defect is set to New, Pending or Retest then the defect is considered blocking.
When a test run receives the status Completed or Cancelled then the Active tester field is cleared.
For more information, see: Keeping order (yes/no)