Add eslint plugin tests

[dartess]

Code change checklist

• [x] 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[bot]]

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Latest commit: 4e14aa3a9a1495a51790a8887dd48dd701cbe7bf

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[mweststrate]

Thanks!