Fill in the blank below.

The goal of $\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ testing is to validate the functionality and behavior of the system based on its inputs and expected outputs, without considering its internal implementation details. Testers focus on testing the system as a whole, simulating different usage scenarios and ensuring that it performs correctly according to the specified requirements or user expectations.

$*$Please write your answer in lowercase and ensure spelling is correct.