Currently our CI system tests the default features of each port. That is good for finding most failures that are likely to happen, but there is still a fairly high likelihood of bugs slipping into features of each port that our CI doesn't find, because we only test defaults.

We wouldn't want to change to trying to test all features, first because some features are platforms specific so we'd get false failures, and second because that just changes the set of bugs we find: today we miss optional-features-being-broken, that would make us miss default-features-being broken.

In general, we can't test every combination of features, but we might want to test more, or at least more combinations for ports in which we have seen such features create customer failures in the past.