What is another word for a surprise test?

Here are some words that could be used instead of "surprise test":

Formal:

* Pop quiz

* Unannounced assessment

* Unscheduled test

* Sudden examination

* Impromptu test

Informal:

* Pop quiz (most common)

* Surprise quiz

* Blindsided test

* Catch-you-off-guard test

* Gotcha test

The best word to use will depend on the context and the level of formality you want to convey.