..., the big one being that Catch2 is no longer a single-header library. Catch2 now behaves as a normal library, with multiple headers and separately compiled implementation. Quick and easy to get started. Just download two files, add them to your project and you're away. No external dependencies. As long as you can compile C++14 and have the C++ standard library available. Write test cases as, self-registering, functions (or methods, if you prefer).