If you call `project.includes_contributors?(["contribA", "contribB"])` I imagine you want it to return true if A and B are already listed as contributors in the project.
However, if I'm not mistaken, a.subset?(b) checks that b is a superset of a.
That is, if the contributors in the project are `["contribA", "contribB", contribC"]`, and you want to check if A and B are included, you'll have this code:
`["contribA", "contribB", "contribC"].subset?(["contribA", "contribB"])`

Which would return `false` when you want it to return `true`.