You have found Roact’s test cases. Roact uses TestEZ to make sure after any update their library still works correctly. These tests basically try and simulate an action to make sure it still returns the correct info.
Here is the github link GitHub - Roblox/testez: BDD-style test and assertion library for Roblox Lua
And here is the API API Reference - TestEZ Documentation
Additionally if you are looking to implement tests into your own game, there is a neat little plugin that can help you linked here.