diff --git a/IPython/nbconvert/filters/strings.py b/IPython/nbconvert/filters/strings.py
index bd05c9f..40f924e 100755
--- a/IPython/nbconvert/filters/strings.py
+++ b/IPython/nbconvert/filters/strings.py
@@ -19,6 +19,7 @@ templates.
 import re
 import textwrap
 from xml.etree import ElementTree
+from types import StringTypes
 
 from IPython.utils import py3compat
 
@@ -61,11 +62,7 @@ def html_text(element):
     
     Analog of jQuery's $(element).text()
     """
-    instance_element_tree = isinstance(ElementTree.ElementTree, type) and \
-                            isinstance(element, (ElementTree.ElementTree))
-    instance_element = isinstance(ElementTree.Element, type) and \
-                       isinstance(element, (ElementTree.Element))
-    if not (instance_element or instance_element_tree):
+    if isinstance(element, StringTypes):
         element = ElementTree.fromstring(element)
     
     text = element.text or ""
diff --git a/IPython/nbconvert/tests/base.py b/IPython/nbconvert/tests/base.py
index b5f4582..cfd7c62 100644
--- a/IPython/nbconvert/tests/base.py
+++ b/IPython/nbconvert/tests/base.py
@@ -18,6 +18,7 @@ import subprocess
 import os
 import glob
 import shutil
+import sys
 
 import IPython
 from IPython.utils.tempdir import TemporaryDirectory
@@ -166,5 +167,5 @@ class TestsBase(object):
 
 
     def call(self, parameters):
-        return subprocess.check_output(parameters)
+        return subprocess.Popen(parameters, stdout=subprocess.PIPE).communicate()[0]
      
\ No newline at end of file