Which technique is used to test software solutions where inputs and expected outputs are known but the internal processes are not?

The technique referred to in this scenario is known as black box testing. This approach focuses on testing the functionality of the software based solely on the inputs and expected outputs, without any knowledge of the internal workings or code structure of the application.

In black box testing, the tester is concerned with the behavior of the software and whether it meets the specified requirements or performs as intended. This method allows for the evaluation of software from the end-user's perspective, ensuring that the software actually meets their needs and behaves correctly for various input conditions.

In contrast, the other techniques involve different levels of insight into the internal processes of the software. For instance, unit testing typically focuses on individual components or functions and requires knowledge of the code. White box testing involves examining the internal logic and structure of the code, while integration testing is about assessing the interactions between different components and how they work together. In all these cases, an understanding of the internal workings is necessary, which differentiates them from black box testing.