That's my criterion on whether external references should be allowed in tests. A surgeon should know their specialty as they won't have time to consult a reference during a surgery. A physicist will always have the time to refer to something when performing their work, as will an editor or teacher.
That's entirely different from saying they don't need to learn it however. If I drop a list of 100 formulas and equations on a person who doesn't know how to use them, they're useless. That background knowledge on what's available and how to use the tools you have is what the class should be teaching you.
Or as my physics prof used to say, "I want the engineer building the bridge I drive over to have looked up a reference on the static weight load of the materials selected, not pulling figures out of their head".
We were always allowed to use 1 standard sheet of paper, front & back, for our tests. Most of the time you could answer most questions without needing them beyond referring to a specific equation to make sure you weren't leaving off a constant (damn factors of 2....).