diff --git a/test/graphics/document_test.rb b/test/graphics/document_test.rb
index 7993916..14d9634 100644
--- a/test/graphics/document_test.rb
+++ b/test/graphics/document_test.rb
@@ -63,8 +63,8 @@ def setup
       def teardown = setup
 
       def test_class_relations
-        UNRELATED.each { |klass| refute(klass <= Document::Default) }
-        RELATED.each   { |klass| assert(klass <= Document::Default) }
+        UNRELATED.each { |klass| refute_operator(klass, :<=, Document::Default) }
+        RELATED.each   { |klass| assert_operator(klass, :<=, Document::Default) }
       end
 
       def test_method_missing_caching_with_block