A test head assembly for supporting at least a portion of a protective mask to be tested for leaks. Preferably, the test head assembly includes a test head having a test space that is generally coextensive with an inner surface of the protective mask being tested. Although the test space is generally coextensive with the inner surface of the protective mask being tested, it is designed such that it has minimal volume to enhance the testing process by expediting test response time, reducing the time period it takes for a mask tester to reach one or more prerequisite test conditions, eliminate or greatly reduce lag time when the mask tester is operating in the probe mode and prevent dilution of challenge concentration. Preferably, the test head is formed from two or more removable sections to allow the size of the test head to be readily modified.