1 files changed, 13 insertions, 0 deletions
diff --git a/src/beautifulsoup/builder/__init__.py b/src/beautifulsoup/builder/__init__.py
index cf54c9c..b7db8db 100644
--- a/src/beautifulsoup/builder/__init__.py
+++ b/src/beautifulsoup/builder/__init__.py
@@ -26,6 +26,19 @@ class TreeBuilder(Entities):
     def feed(self, markup):
         raise NotImplementedError()
 
+    def test_fragment_to_document(self, fragment):
+        """Wrap an HTML fragment to make it look like a document.
+
+        Different parsers do this differently. For instance, lxml
+        introduces an empty <head> tag, and html5lib
+        doesn't. Abstracting this away lets us write simple tests
+        which run HTML fragments through the parser and compare the
+        results against other HTML fragments.
+
+        This method should not be used outside of tests.
+        """
+        return fragment
+
 
 class SAXTreeBuilder(TreeBuilder):
     """A Beautiful Soup treebuilder that listens for SAX events."""