Test Client shouldn't subclass RequestFactory

[Ana Balica]

Currently the test Client is inheriting from RequestFactory for code reuse. Client is not a specialisation of the RequestFactory and the relationship between the two is conceptually incorrect.

Much easier would be to use composition. With that it also becomes possible to use any other type of request factory with the Client. Open for discussion if there is actually any need for a different request factory besides the default one.

[Tim Graham]

I'm not sure I understand the motivation or exactly how things would change. For reference, eec45e8b710b97201db106a6460fe051f8917833 is the commit that created RequestFactory.

[Ana Balica]

This is a design improvement. Now besides using composition by initialising the RequestFactory in Client's __init__, it's also possible to pass your own custom request factory to be used by the client. A possible use case for having a custom factory of requests is to test against HTTP/2.0. Even though this is not a strong argument I still consider it a good improvement, that makes a lot sense.

Backwards compatibility considerations: I've checked the codebase of ​pytest-django, ​django-nose and ​django-test-plus and it doesn't seem like anyone is hacking the Client, so the following change shouldn't break others' code. However there must be someone who isn't going to be happy :(

I'm thinking to document this behaviour as it might be useful for others.

[Tim Graham]

WIP ​PR

[Ana Balica]

By introducing some design changes got a more confusing API for Client and RequestFactory.
Also proper way of fixing that would break other people's code too much. Not worth it.