Create tests for webhooks

[jeremystretch]

Proposed Changes

Create new unit tests for:

1. Create/updating/deleting webhooks
2. Placing webhook events in the queue
3. Transmitting webhooks

Justification

We have a huge gap in our test coverage around webhooks currently, leading to bugs such as #3951.

[jeremystretch]

I've added tests for the enqueuing process in c6eb40d, but I'm not sure how to go about testing the RQ worker process. @lampwins any ideas?

[hSaria]

unittest.mock.patch the requests.send and checking it is called with the expected arguments is an option (I was testing with requests.post, but you get the idea).

>>> from unittest.mock import patch
>>> import requests
>>>
>>> def send():
...     requests.post('http://localhost')
... 
>>> @patch('requests.post')
... def test_send(mock_post):
...     send()
...     mock_post.assert_called_with('http://localhost')
... 
>>> test_send()
>>> 
>>> def send():
...     requests.post('http://not_localhost')
... 
>>> test_send()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python/3.7.6_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/unittest/mock.py", line 1255, in patched
    return func(*args, **keywargs)
  File "<stdin>", line 4, in test_send
  File "/usr/local/Cellar/python/3.7.6_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/unittest/mock.py", line 873, in assert_called_with
    raise AssertionError(_error_message()) from cause
AssertionError: Expected call: post('http://localhost')
Actual call: post('http://not_localhost')
>>>