I have the following (simplified) Rails Concern:
module HasTerms
extend ActiveSupport::Concern
module ClassMethods
def optional_agreement
# At
You could just test the module implicitly by leaving your tests in the classes that include this module. Alternatively, you can include other requisite modules in your dummy class. For instance, the validates methods in AR models are provided by ActiveModel::Validations. So, for your tests:
class DummyClass
include ActiveModel::Validations
include HasTerms
end
There may be other modules you need to bring in based on dependencies you implicitly rely on in your HasTerms module.