test/user_types: enforce testing of matmul operation

unittest/python/test_user_type.py

@@ -32,6 +32,9 @@ def test(dtype):
   assert not (mat > mat).all()
   assert not (mat < mat).all()
 
+  mat2 = mat.dot(mat.T)
+  mat2 = np.matmul(mat,mat.T)
+
 def test_cast(from_dtype,to_dtype):
   np.can_cast(from_dtype,to_dtype)