MockResponse has to be refactored

[foursixnine]

There is some repeated code that is very tightly coupled to its module:

tests/test_incident.py # being added by #154 
133:    class MockResponse:
141:        return MockResponse(

tests/test_incidents.py 
109:    class MockResponse:
116:        return MockResponse()

tests/test_aggregate.py
52:    class MockResponse:
59:        return MockResponse()

That can be extracted into its own utility, so the caller can specify what's the expected output in a more generic way

[okurz]

Might be possible to refactor this however for test code itself more commonly it is preferred to be a bit more explicit and hence allow some duplication. But let's see how it would look like if somebody proposes such refactoring in a pull request.

[foursixnine]

This would be a good easy fix, maybe easyfix, hacktoberfest

[LakshayPuhal]

I would like to work on this issue.