Add eslint plugin tests

[dartess]

Code change checklist

• Added/updated unit tests
• Updated /docs. For new functionality, at least API.md should be updated
• Verified that there is no significant performance drop (yarn mobx test:performance)

I would like to work on the plugin in the future, so I started simple - adding TODO tests

[changeset-bot]

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Latest commit: 4e14aa3

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[mweststrate]

Thanks!