CDIMixIn and TransactionMixIn has its participant interface and looking for the mixin implements that interface from @MixInDependencies. But as we can retrieve a list of mixins from testkit, participant class doesn't have to use @MixInDependencies, all it has to do is just iterate all the mixins and test if it implements participant interface. Plus although TransactionMixIn implements CDIMixInParticipant, as CDIMixIn doesn't have TransactionMixIn in its @MixInDependencies/optional, TransactionMixIn#participate() is never invoked. That will also be solved by removing @MixInDependencies usage from this participant stuff.