Add tests for block plugin

Problem/Motivation

The feedback module's custom block plugin has a number of controls for customizing how feedback is gathered. Specifically, it controls...

1. Feedback type
2. Help text
3. Submit button

Proposed resolution

We should make sure the block plugin has a test so that we can be sure it doesn't regress.

Remaining tasks

1. Write a merge request
2. Review and feedback
3. RTBC and feedback
4. Commit

User interface changes

None.

API changes

None.

Data model changes

None.