Final answer:
The security professional is engaged in black-box testing, a method where the application's functionality is tested without knowledge of the internal code, focusing on input and output behaviors.
Step-by-step explanation:
A security professional who is testing the functionality of an application without any knowledge about the internal coding is performing a type of testing known as black-box testing. This method evaluates the application from an external perspective, focusing on inputs and the expected outputs without knowing how the application processes the data internally.
Black-box testing can involve functional testing, system testing, and acceptance testing among other approaches. It is crucial for validating the correctness of an application's functionality.
Black-box testing contrasts with white-box testing, where the tester has an in-depth knowledge of the internal code structure. Another related method is grey-box testing which is a combination of both approaches, where some knowledge about the internal workings is known but not to the extent of white-box testing.