Assertion

In software testing, an assertion is that a specific condition should be true at a particular point in the code's execution. 

It's a way to verify that the code is behaving as expected. If the assertion fails (the condition is false), it indicates a bug or an unexpected behavior. 

Assertions are commonly used in unit testing frameworks to check the results of a test. For example, you might assert that the value returned by a function is equal to the expected value. 

In general, the assertion is the last part of the test, if the condition is met the test passes. It’s a good idea not to assert too different many things in one test, ideally, we want it to have a single point of failure so it’s easier to debug