Update tests.

Also add an assertion for symptom of html5lib#217 (without this the
testsuite goes into an infinite loop; this doesn't fix the cause
but it avoids the infinite loop happening!).

Author: gsnedders

.pytest.expect

@@ -129,6 +129,7 @@ def getParentNode(self, node):
                 if not parents:
                     return parent
                 else:
+                    assert list(parents[-1]).count(parent) == 1
                     return parent, list(parents[-1]).index(parent), parents, None
 
     return locals()