Drager tubes do not need to be tested. It is the drager pump that need to be tested for "Leak Test".
Now depending upon the model of drager pump, the leak test procedure could be different. Let us see how to do the Leak test with Drager Accuro pump which is most common Drager pump. To perform the "Leak test" on Drager Accuro pump, connect a unbroken Drager tube to the Drager pump.
Squeeze the Drager pump completely and then release it. The bellow of the pump should remain in vacuum for 10-15 minutes. There is also a dot which when white indicates that the bellow is in Vacuum and when black it indicates that the bellow is not in Vacuum.
Another Model of the Drager may have inbuilt leak test function.
But if you are looking to test if the Drager tube would measure and give correct readings or not, I don't think there is any way to test that and we are not required to test that.