In tests/tests.lisp, there are several definitions of methods for c2mop:direct-slot-definition-class, all of them with &key in the lambda list. This is wrong, because the lambda list of c2mop:direct-slot-definition-class is (class &rest initargs)https://clos-mop.hexstreamsoft.com/generic-functions-and-methods/.
With the &key, it means it doesn't allow any keys, so gives an error when the implemtation actually checks (because at least the name is in the initargs).