Er/test fusion

[emmyoop]

resolves #

Problem

This is very much a WIP!

Solution

Add testing for the fusion engine.

Note: https://github.com/dbt-labs/dbt-package-testing/pull/12 currently only supports testing on snowflake.

Checklist

• [ ] This code is associated with an issue which has been triaged and accepted for development.
• [ ] I have read the contributing guide and understand what's expected of me
• [ ] I have run this code in development and it appears to resolve the stated issue
• [ ] This PR includes tests, or tests are not required/relevant for this PR
• [ ] I have updated the README.md (if applicable)

[dbeatty10]

Closing and re-opening to re-trigger CI