Fix file imports integration tests

[cydanil]

Description

This PR fixes imports from supported formats tests, and adds a test for the mycookbook file format.
This also closes thinkle/gourmet #1014

How Has This Been Tested?

These tests were ran using pytest and are now part of the CI.

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 not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.