assertRedirects gives unhelpful error message expected URL is external

[Peter Inglesby]

assertRedirects uses the test client and so cannot fetch external URLs. When the expected URL is set to an external URL, assertRedirects fails with something like:

AssertionError: 404 != 200 : Couldn't retrieve redirection page '/some-path/': response code was 404 (expected 200)

It would be better if assertRedirects could detect that it was being used incorrectly, and gave a more helpful error message.

[Tim Graham]

The message could suggest using the fetch_redirect_response=False argument.

[Markus Holtermann <info@…>]

In c7b1b81:

Fixed #26666 -- Added more useful error message to assertRedirects

[Tim Graham]

Tobias is working on fixing the test failures that the patched introduced.

[Markus Holtermann <info@…>]

In 78a0ca6:

Refs #26666 -- Fixed test failures caused by assertRedirects changes (#6701)

[Tobias McNulty]

• The original fix to this ticket (​https://github.com/django/django/pull/6696) broke unit testing of custom hostnames in non-core Django projects when the hostname was passed as part of the path to client.get()
• A new proposed change (​https://github.com/django/django/pull/6713) leverages ALLOWED_HOSTS to facilitate support for custom domain testing in 3rd party packages while increasing the rigor which with we validate ALLOWED_HOSTS (now also in tests)

[Simon Charette]

The code part LGTM but the doc could benefit from a second look of a native speaker.

[Philip James]

As a native speaker I took a look over the docs, and they make a lot of sense minus one potentially confusing bit. I left a comment on the PR.

[Tim Graham <timograham@…>]

In 17e66164:

Refs #26666 -- Added ALLOWED_HOSTS validation when running tests.

Also used ALLOWED_HOSTS to check for external hosts in assertRedirects().