One of the weirdest errors out there, and as far as I know we're the only ones suffering from it, due to having multiple packages of Python bindings created with Sip as well as having PyQt and different threads.
This obscure error happens when a module with Sip bindings is being imported after PyQt. Due to a clash with the Sip versions or something, it then fails on the custom module. Import all of our custom modules with Sip bindings first.
Delete a test that needs a ContainerProvider. We need to discuss if we
want to add it back, depending if we are still keeping the providers.
Contributes to CURA-5628.