Use assert_empty for empty string assertion

Author: tompng

test/rdoc/rdoc_parser_c_test.rb

@@ -1628,7 +1628,7 @@ def test_look_for_directives_in
 
     parser.look_for_directives_in @top_level, comment
 
-    assert_equal "", comment.text
+    assert_empty comment.text
     assert_equal 'not_handled', @top_level.metadata['other']
   end
 

test/rdoc/rdoc_parser_simple_test.rb

@@ -26,7 +26,7 @@ def test_initialize_metadata
 
     assert_includes @top_level.metadata, 'unhandled'
 
-    assert_equal "", parser.content
+    assert_empty parser.content
   end
 
   def test_remove_coding_comment