add test

Author: ablaom

test/traits.jl

@@ -50,6 +50,7 @@ small = SmallLearner()
 
 @trait SmallLearner kinds_of_proxy=(Point(),)
 @test LearnAPI.is_learner(small)
+@test !LearnAPI.is_learner("junk")
 @test !LearnAPI.target(small)
 @test !LearnAPI.weights(small)
 @test LearnAPI.preferred_kind_of_proxy(small) == Point()