Make it possible to disable exception re-raising in test client

[Carl Meyer]

In the Django test client, we connect to the got_request_exception signal, store any signalled exception on the test client, and then after the response is returned, we check for a signalled exception and re-raise it (​https://github.com/django/django/blob/master/django/test/client.py#L492-L495). Fair enough; usually in tests you prefer to have the exception raised instead of just seeing a 500 error.

But there are two problems with this: 1) it's impossible to turn off (and sometimes there are times when you'd want to, e.g. if testing behavior of handle_uncaught_exception in a custom WSGI handler subclass), and 2) Django has long had an alternate method to do exactly the same thing, the DEBUG_PROPAGATE_EXCEPTIONS setting.

The setting is much simpler, and it's easy to turn off for a selected test.

I think we should at least provide a way to turn off the test client re-raising behavior (perhaps via a flag set on the client).

I'm tempted to suggest we should also at some point raise a deprecation warning if this flag is not set, suggesting to use DEBUG_PROPAGATE_EXCEPTIONS when running tests instead, and then later remove the test-client re-raising altogether. But removing this bit of code may not be worth the churn of that deprecation.

[Tim Graham]

Would you consider this a duplicate of #18707? The solution you proposed about adding an option to Client is proposed in comment 1.

[Carl Meyer]

Yeah, it's a duplicate - thanks!