Can a pinhole test determine if you have lazy eye or not?

Maybe: The pinhole test is a rapid screening technique to check for gross focusing errors in the eyes. If the vision improves dramatically with a pinhole we at least know the amblyopia isn't too severe. The only real way to quantify it is to do a refraction with a device called a phoropter which uses real lenses.

Not definitively: Pinhole helps to test for any refractive error, and can help predict best potential acuity (pap). Lazy eye amblyopia is defined: DX of exclusion, once the visual pathway is determined to be ok but the vision is still limited due to developmental changes in the brain visual cortex.