Previously, the responses set in bot test fixtures
where handled as JSON objects. This works fine for
most bot tests, because most of the APIs that bots
are calling return a JSON-formatted response object.
However, some, like Trello, do return raw data.
This hasn't been noticed so far, because the respective
Trello test needed internet access. Tests shouldn't
need internet access.
This commit makes that Trello test use a fixture. To
work properly, it also adds a way to make http_mock_config
parse the response object as raw data.
This can now be done by modifying the "is_raw_response"
property in a newly introduced "meta" object that can
be used to specify how a fixture should be handled.
This commit changes 'Mock.assert_called()' to 'assert Mock.called'.
This is needed because in unittest.mock, assert_called() is only
supported in Python >=3.6.
The new module mocks out calls to the requests library, which
is used by many of our bots that use third party services.
Mocking of requests.py is mostly orthogonal to our other
testing concerns.
