Add explicit test for the logging notifier middleware

[LucasRoesler]

Description

• Add unit test that verifies the behavior of the logging middleware in
  various response cases

Motivation and Context

• I have raised an issue to propose this change (required)
• My issue has received approval from the maintainers or lead with the design/approved label

An issue with logging came up in Slack and this shows that the issue is not in the notification or logging middlewares

How Has This Been Tested?

It is a unit test

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.

[alexellis]

Approved