Im surprised to hear that. I went to Caltech for my postgrad and never collaborated on an test, and it would have never ocurre me to do so (and no, the professor didn’t have to explicitly say they collaboration was not allowed. It was just the standard honor code).

We all suspected of people that didn’t adhere to the honor code and it was frowned upon, and they could have faced repercussions if anyone had reported them.

I did ChemE for undergrad and aerospace focused on systems engineering for postgrad so that colored my experience a bit. The former was brutal and the latter naturally collaborative with a bunch of projects, so we all worked together.

The postgrad continuum mechanics class (I think taught by the geophysics department?) was the biggest exception so I’m betting there’s quite a bit of variance among fields.

I don’t doubt there’s academic fraud (living in the dorm my first year wiped away any illusion) but within my major it didn’t end well.