The standard way to test your clutch is to see if it will hold high torque at low rpm.
First try this: Drive at 40 mph in 5th and just floor it in gear. If the clutch slips you know it's really in bad shape and must be replaced.
If it didn't slip by just flooring it then try this more aggressive test: Take the car out on an open road and go about 40 mph with the car in 5th gear. Push in the clutch pedal and then while coasting simultaneously drop the clutch and floor the gas. If the rpm drops right down to what it should be in 5th gear with the car accelerating normally, your clutch is ok. If the rpm starts rapidly climbing beyond what it would normally do in 5th and the car not accelerating normally, your clutch is shot.