Create common pattern for unit/integration testing

[LauJohansson]

In order to streamline how we do testing we need a common way of doing unit/integration tests.

How do we:

• Do unittest
• Do integrationstest
• Do hybrids (test ETL with mocked data)
• Get "more clear" definitions of unittest/integrationtest
• How to handle tests of data extraction from storage account? e.g. the eventhubcapture extractor.

[LauJohansson]

Ideas for decorating and testing exceptions: https://testfixtures.readthedocs.io/en/latest/exceptions.html#the-should-raise-decorator

Same with warnings: https://testfixtures.readthedocs.io/en/latest/warnings.html#the-shouldwarn-context-manager