A method and a testing device (1) function test a vibration motor (2) arranged in a portable gas-measuring device (3). A sensor (4) detects a value for a motor property transmits the value to a control and analysis unit (5). The detected value is compared with a desired value, a test result is generated on the basis of the comparison, and a trigger signal is generated on the basis of the test result. A terminal voltage and/or current are determined during a switching-on and/or switching-off operation of the vibration motor (2) at an electrical terminal (6) of the vibration motor (2) on the basis of the motor property of the vibration motor (2). This terminal voltage and/or the terminal current present at least at times during the switching-on and/or switching-off operation are compared with at least one desired value in the control and analysis unit (5).