Add input completion test suite (#4644)

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/providers/twitch/api/README.md

@@ -12,7 +12,7 @@ If you're adding support for a new endpoint, these are the things you should kno
 
 1. Add a virtual function in the `IHelix` class. Naming should reflect the API name as best as possible.
 1. Override the virtual function in the `Helix` class.
-1. Mock the function in the `MockHelix` class in the `tests/src/HighlightController.cpp` file.
+1. Mock the function in the `mock::Helix` class in the `mocks/include/mocks/Helix.hpp` file.
 1. (Optional) Make a new error enum for the failure callback.
 
 For a simple example, see the `updateUserChatColor` function and its error enum `HelixUpdateUserChatColorError`.