In experiments it is easy to discern between 2 and more-than-2 fringes on a screen, making the double-slit experiment the default one for wave-particle tests.
Let's say we shoot massive particles (e.g. electrons) towards a slit. Would the image behind it be the same no matter if we consider the electrons to be classical particles or wave-packets?
My interpretation, using an ideal (infinitely-narrow) slit, is that the (interpretation of the particles as) classical particles would produce an image with sharp boundaries, while a wave would imprint a gaussian-like distribution on the screen.