Fail integration test on missing mock
Created by: felixfbecker
This fixes almost all tests that were missing mocks and enforces all requests to be mocked going forward. Integration tests were basically impossible to debug before this PR. It even caused confusion on other teams recently: https://sourcegraph.slack.com/archives/C07KZF47K/p1602264139259700?thread_ts=1602262753.257900&cid=C07KZF47K