3 files changed, 21 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."""
diff --git a/src/beautifulsoup/builder/html5lib_builder.py b/src/beautifulsoup/builder/html5lib_builder.py
index b4ef4de..80c3e6d 100644
--- a/src/beautifulsoup/builder/html5lib_builder.py
+++ b/src/beautifulsoup/builder/html5lib_builder.py
@@ -21,4 +21,7 @@ class HTML5TreeBuilder(SAXTreeBuilder, HTMLTreeBuilder):
         walker = treewalkers.getTreeWalker('dom')
         dom2sax(doc, self)
 
+    def test_fragment_to_document(self, fragment):
+        """See `TreeBuilder`."""
+        return u'<html><head></head><body>%s</body></html>' % fragment
 
diff --git a/src/beautifulsoup/builder/lxml_builder.py b/src/beautifulsoup/builder/lxml_builder.py
index 4949fea..3e1de5f 100644
--- a/src/beautifulsoup/builder/lxml_builder.py
+++ b/src/beautifulsoup/builder/lxml_builder.py
@@ -29,3 +29,8 @@ class LXMLTreeBuilder(HTMLTreeBuilder):
         self.soup.endData()
         self.soup.handle_data(content)
         self.soup.endData(Comment)
+
+    def test_fragment_to_document(self, fragment):
+        """See `TreeBuilder`."""
+        return u'<html><body>%s</body></html>' % fragment
+