To perform multiple test runs simultaneously on the same machine, you must specify for each mysql-test-run.pl invocation which ports to use so that no test run conflicts with others running concurrently. To do this, add unique port arguments to mysql-test-run.pl, such as --master_port=3911 --slave_port=3927 --no-manager.

Only one instance of mysql-test-run.pl can run at a time in the same mysql-test directory on a shared drive. The mysql-test/var directory created and used by mysql-test-run.pl cannot be shared between simultaneous test runs. A test run can use the --var=dir_path option to specify an alternate directory not used by other runs.