Integration tests are for determining that different parts of the framework will work
together (integrate) as expected. An example of a common integration test would be for
ensuring that an adapter interacts correctly with the class it is designed to interface
with. Example: the `Session` class and the `Php` adapter. Unit tests will ensure that
both the `Session` and `Php` classes behave correctly under isolation, while an integration
test ensures that the two classes interact and interface correctly.