Upgrade custom nav

[rtibbles]

Summary

• Allow upgrade of custom nav items
• Slight refactor of Remote Channel viewset and Remote Channel Resource to return a single item on Model fetch.

Reviewer guidance

Can you upgrade to a newer version of a custom nav channel?

I tested this by upgrading, and then confirming that the new zip file was marked as available in my DB and also that it was my content storage folder.

---

Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[jonboiser]

The tests are failing because the mock of /api/remotechannel still returns arrays.
https://github.com/learningequality/kolibri/pull/8039/checks?check_run_id=2461892526#step:6:423

I don't know if it's possible, but it would create a stronger test to mock the response from Studio itself, rather than mocking the internals of RemoteChannelViewset

[rtibbles]

mock the response from Studio itself, rather than mocking the internals of RemoteChannelViewset

From what I can see that is what the test is doing:

def mock_patch_decorator(func):
    def wrapper(*args, **kwargs):
        mock_object = mock.Mock()
        mock_object.json.return_value = [{"id": 1, "name": "studio"}]
        with mock.patch.object(requests, "get", return_value=mock_object):
            return func(*args, **kwargs)

    return wrapper

This is mocking the requests get that happens inside the response, so mocking the Studio response.

[jonboiser]

Ah, I thought mocking requests was somehow affecting the TestCase client, but they are obviously different.

[rtibbles]

Yeah, we (unusually) use requests inside the RemoteChannelViewset to then do the subsequent fetch against Studio.

[jonboiser]

looks good!

[jredrejo]

@rtibbles , @jonboiser the changes in https://github.com/learningequality/kolibri/blob/develop/kolibri/core/content/api.py#L982 is breaking importing channels from studio , due to this commit: 585e5cc

ERROR    Internal Server Error: /api/content/remotechannel/nakav-mafak/retrieve_list/
Traceback (most recent call last):
  File "/datos/le/mio/kolibri/venv/lib/python3.8/site-packages/django/core/handlers/exception.py", line 41, in inner
    response = get_response(request)
  File "/datos/le/mio/kolibri/venv/lib/python3.8/site-packages/django/core/handlers/base.py", line 187, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/datos/le/mio/kolibri/venv/lib/python3.8/site-packages/django/core/handlers/base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/datos/le/mio/kolibri/venv/lib/python3.8/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
    return view_func(*args, **kwargs)
  File "/datos/le/mio/kolibri/venv/lib/python3.8/site-packages/rest_framework/viewsets.py", line 116, in view
    return self.dispatch(request, *args, **kwargs)
  File "/datos/le/mio/kolibri/venv/lib/python3.8/site-packages/rest_framework/views.py", line 497, in dispatch
    self.response = self.finalize_response(request, response, *args, **kwargs)
  File "/datos/le/mio/kolibri/venv/lib/python3.8/site-packages/rest_framework/views.py", line 409, in finalize_response
    assert isinstance(response, HttpResponseBase), (
AssertionError: Expected a `Response`, `HttpResponse` or `HttpStreamingResponse` to be returned from the view, but received a `<class 'list'>`

[rtibbles]

Ah, looks like I forgot to wrap one in a response.

[rtibbles]

Thanks @jredrejo have fixed it here: #8042