Scientist can either use experiments or models for example (most common ways):
Experiments - consist in recreating the scene or whatever wants to be tested, and see if they're predictions matched.
Models - if the predictions are related to an object for example, scientists can create a miniature, or depending on what needs to be tested, a non-complete object. Models though, can be used the same way as experiments.
Hope it helped,
Happy homework/ study/ exam!
