A testing apparatus and method for characterizing the aerodynamic particle size of an atomized medicament emitted from a metered dose inhaler unit during testing with a particle characterization device in which the testing apparatus includes a first clamp of a first fixture in removable clamping and locking engagement with a throat, which is in fluid communication with a particle characterization device, a second clamp in removable clamping and locking engagement with a delivery device of the metered dose inhaler unit having a canister, containing atomized medicament, operatively loaded therein, an alignment mechanism that removably couples the first fixture to the second fixture at an aligned position therefore causing the throat to be in fluid communication with the delivery device, and an actuation assembly mounted to the first fixture having means that operatively thrusts the canister into the delivery device of the metered dose inhaler unit, thus releasing atomized medicament .