diff --git a/common/lib/capa/capa/tests/__init__.py b/common/lib/capa/capa/tests/__init__.py
index 1997e4d055..d989405951 100644
--- a/common/lib/capa/capa/tests/__init__.py
+++ b/common/lib/capa/capa/tests/__init__.py
@@ -22,21 +22,27 @@ def calledback_url(dispatch = 'score_update'):
 xqueue_interface = MagicMock()
 xqueue_interface.send_to_queue.return_value = (0, 'Success!')
 
-test_system = Mock(
-    ajax_url='courses/course_id/modx/a_location',
-    track_function=Mock(),
-    get_module=Mock(),
-    render_template=tst_render_template,
-    replace_urls=Mock(),
-    user=Mock(),
-    filestore=fs.osfs.OSFS(os.path.join(TEST_DIR, "test_files")),
-    debug=True,
-    xqueue={'interface': xqueue_interface, 'construct_callback': calledback_url, 'default_queuename': 'testqueue', 'waittime': 10},
-    node_path=os.environ.get("NODE_PATH", "/usr/local/lib/node_modules"),
-    anonymous_student_id='student',
-    cache=None,
-)
+def test_system():
+    """
+    Construct a mock ModuleSystem instance.
 
-def new_loncapa_problem(xml):
+    """
+    the_system = Mock(
+        ajax_url='courses/course_id/modx/a_location',
+        track_function=Mock(),
+        get_module=Mock(),
+        render_template=tst_render_template,
+        replace_urls=Mock(),
+        user=Mock(),
+        filestore=fs.osfs.OSFS(os.path.join(TEST_DIR, "test_files")),
+        debug=True,
+        xqueue={'interface': xqueue_interface, 'construct_callback': calledback_url, 'default_queuename': 'testqueue', 'waittime': 10},
+        node_path=os.environ.get("NODE_PATH", "/usr/local/lib/node_modules"),
+        anonymous_student_id='student',
+        cache=None,
+    )
+    return the_system
+
+def new_loncapa_problem(xml, system=None):
     """Construct a `LoncapaProblem` suitable for unit tests."""
-    return LoncapaProblem(xml, id='1', seed=723, system=test_system)
+    return LoncapaProblem(xml, id='1', seed=723, system=system or test_system())
diff --git a/common/lib/capa/capa/tests/test_customrender.py b/common/lib/capa/capa/tests/test_customrender.py
index eece275b05..8012804a40 100644
--- a/common/lib/capa/capa/tests/test_customrender.py
+++ b/common/lib/capa/capa/tests/test_customrender.py
@@ -26,7 +26,7 @@ class HelperTest(unittest.TestCase):
     Make sure that our helper function works!
     '''
     def check(self, d):
-        xml = etree.XML(test_system.render_template('blah', d))
+        xml = etree.XML(test_system().render_template('blah', d))
         self.assertEqual(d, extract_context(xml))
 
     def test_extract_context(self):
@@ -46,11 +46,11 @@ class SolutionRenderTest(unittest.TestCase):
         xml_str = """<solution id="solution_12">{s}</solution>""".format(s=solution)
         element = etree.fromstring(xml_str)
 
-        renderer = lookup_tag('solution')(test_system, element)
+        renderer = lookup_tag('solution')(test_system(), element)
 
         self.assertEqual(renderer.id, 'solution_12')
 
-        # our test_system "renders" templates to a div with the repr of the context
+        # Our test_system "renders" templates to a div with the repr of the context.
         xml = renderer.get_html()
         context = extract_context(xml)
         self.assertEqual(context, {'id': 'solution_12'})
@@ -65,7 +65,7 @@ class MathRenderTest(unittest.TestCase):
         xml_str = """<math>{tex}</math>""".format(tex=latex_in)
         element = etree.fromstring(xml_str)
 
-        renderer = lookup_tag('math')(test_system, element)
+        renderer = lookup_tag('math')(test_system(), element)
 
         self.assertEqual(renderer.mathstr, mathjax_out)
 
diff --git a/common/lib/capa/capa/tests/test_html_render.py b/common/lib/capa/capa/tests/test_html_render.py
index e0edf344f2..62605b48f5 100644
--- a/common/lib/capa/capa/tests/test_html_render.py
+++ b/common/lib/capa/capa/tests/test_html_render.py
@@ -11,6 +11,10 @@ from . import test_system, new_loncapa_problem
 
 class CapaHtmlRenderTest(unittest.TestCase):
 
+    def setUp(self):
+        super(CapaHtmlRenderTest, self).setUp()
+        self.system = test_system()
+
     def test_blank_problem(self):
         """
         It's important that blank problems don't break, since that's
@@ -38,7 +42,7 @@ class CapaHtmlRenderTest(unittest.TestCase):
         """)
 
         # Create the problem
-        problem = new_loncapa_problem(xml_str)
+        problem = new_loncapa_problem(xml_str, system=self.system)
 
         # Render the HTML
         rendered_html = etree.XML(problem.get_html())
@@ -48,9 +52,6 @@ class CapaHtmlRenderTest(unittest.TestCase):
         self.assertEqual(test_element.tag, "test")
         self.assertEqual(test_element.text, "Test include")
 
-
-
-
     def test_process_outtext(self):
         # Generate some XML with <startouttext /> and <endouttext />
         xml_str = textwrap.dedent("""
@@ -116,11 +117,12 @@ class CapaHtmlRenderTest(unittest.TestCase):
         xml_str = StringResponseXMLFactory().build_xml(**kwargs)
 
         # Mock out the template renderer
-        test_system.render_template = mock.Mock()
-        test_system.render_template.return_value = "<div>Input Template Render</div>"
+        the_system = test_system()
+        the_system.render_template = mock.Mock()
+        the_system.render_template.return_value = "<div>Input Template Render</div>"
 
         # Create the problem and render the HTML
-        problem = new_loncapa_problem(xml_str)
+        problem = new_loncapa_problem(xml_str, system=the_system)
         rendered_html = etree.XML(problem.get_html())
 
         # Expect problem has been turned into a <div>
@@ -165,7 +167,7 @@ class CapaHtmlRenderTest(unittest.TestCase):
                 mock.call('textline.html', expected_textline_context),
                 mock.call('solutionspan.html', expected_solution_context)]
 
-        self.assertEqual(test_system.render_template.call_args_list,
+        self.assertEqual(the_system.render_template.call_args_list,
                             expected_calls)
 
 
@@ -226,7 +228,7 @@ class CapaHtmlRenderTest(unittest.TestCase):
         self.assertEqual(span_element.get('attr'), "TEST")
 
     def _create_test_file(self, path, content_str):
-        test_fp = test_system.filestore.open(path, "w")
+        test_fp = self.system.filestore.open(path, "w")
         test_fp.write(content_str)
         test_fp.close()
 
diff --git a/common/lib/capa/capa/tests/test_inputtypes.py b/common/lib/capa/capa/tests/test_inputtypes.py
index 54edb5bf9f..313eb28249 100644
--- a/common/lib/capa/capa/tests/test_inputtypes.py
+++ b/common/lib/capa/capa/tests/test_inputtypes.py
@@ -45,7 +45,7 @@ class OptionInputTest(unittest.TestCase):
         state = {'value': 'Down',
                  'id': 'sky_input',
                  'status': 'answered'}
-        option_input = lookup_tag('optioninput')(test_system, element, state)
+        option_input = lookup_tag('optioninput')(test_system(), element, state)
 
         context = option_input._get_render_context()
 
@@ -92,7 +92,7 @@ class ChoiceGroupTest(unittest.TestCase):
                  'id': 'sky_input',
                  'status': 'answered'}
 
-        the_input = lookup_tag(tag)(test_system, element, state)
+        the_input = lookup_tag(tag)(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -142,7 +142,7 @@ class JavascriptInputTest(unittest.TestCase):
         element = etree.fromstring(xml_str)
 
         state = {'value': '3', }
-        the_input = lookup_tag('javascriptinput')(test_system, element, state)
+        the_input = lookup_tag('javascriptinput')(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -170,7 +170,7 @@ class TextLineTest(unittest.TestCase):
         element = etree.fromstring(xml_str)
 
         state = {'value': 'BumbleBee', }
-        the_input = lookup_tag('textline')(test_system, element, state)
+        the_input = lookup_tag('textline')(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -198,7 +198,7 @@ class TextLineTest(unittest.TestCase):
         element = etree.fromstring(xml_str)
 
         state = {'value': 'BumbleBee', }
-        the_input = lookup_tag('textline')(test_system, element, state)
+        the_input = lookup_tag('textline')(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -236,7 +236,7 @@ class TextLineTest(unittest.TestCase):
             element = etree.fromstring(xml_str)
 
             state = {'value': 'BumbleBee', }
-            the_input = lookup_tag('textline')(test_system, element, state)
+            the_input = lookup_tag('textline')(test_system(), element, state)
 
             context = the_input._get_render_context()
 
@@ -274,7 +274,7 @@ class FileSubmissionTest(unittest.TestCase):
                  'status': 'incomplete',
                  'feedback': {'message': '3'}, }
         input_class = lookup_tag('filesubmission')
-        the_input = input_class(test_system, element, state)
+        the_input = input_class(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -319,7 +319,7 @@ class CodeInputTest(unittest.TestCase):
                  'feedback': {'message': '3'}, }
 
         input_class = lookup_tag('codeinput')
-        the_input = input_class(test_system, element, state)
+        the_input = input_class(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -368,7 +368,7 @@ class MatlabTest(unittest.TestCase):
                  'feedback': {'message': '3'}, }
 
         self.input_class = lookup_tag('matlabinput')
-        self.the_input = self.input_class(test_system, elt, state)
+        self.the_input = self.input_class(test_system(), elt, state)
 
     def test_rendering(self):
         context = self.the_input._get_render_context()
@@ -396,7 +396,7 @@ class MatlabTest(unittest.TestCase):
                  'feedback': {'message': '3'}, }
         elt = etree.fromstring(self.xml)
 
-        the_input = self.input_class(test_system, elt, state)
+        the_input = self.input_class(test_system(), elt, state)
         context = the_input._get_render_context()
 
         expected = {'id': 'prob_1_2',
@@ -423,7 +423,7 @@ class MatlabTest(unittest.TestCase):
                      }
             elt = etree.fromstring(self.xml)
 
-            the_input = self.input_class(test_system, elt, state)
+            the_input = self.input_class(test_system(), elt, state)
             context = the_input._get_render_context()
             expected = {'id': 'prob_1_2',
                         'value': 'print "good evening"',
@@ -448,7 +448,7 @@ class MatlabTest(unittest.TestCase):
                  }
         elt = etree.fromstring(self.xml)
 
-        the_input = self.input_class(test_system, elt, state)
+        the_input = self.input_class(test_system(), elt, state)
         context = the_input._get_render_context()
         expected = {'id': 'prob_1_2',
                     'value': 'print "good evening"',
@@ -470,7 +470,7 @@ class MatlabTest(unittest.TestCase):
         get = {'submission': 'x = 1234;'}
         response = self.the_input.handle_ajax("plot", get)
 
-        test_system.xqueue['interface'].send_to_queue.assert_called_with(header=ANY, body=ANY)
+        test_system().xqueue['interface'].send_to_queue.assert_called_with(header=ANY, body=ANY)
 
         self.assertTrue(response['success'])
         self.assertTrue(self.the_input.input_state['queuekey'] is not None)
@@ -479,13 +479,12 @@ class MatlabTest(unittest.TestCase):
     def test_plot_data_failure(self):
         get = {'submission': 'x = 1234;'}
         error_message = 'Error message!'
-        test_system.xqueue['interface'].send_to_queue.return_value = (1, error_message)
+        test_system().xqueue['interface'].send_to_queue.return_value = (1, error_message)
         response = self.the_input.handle_ajax("plot", get)
         self.assertFalse(response['success'])
         self.assertEqual(response['message'], error_message)
         self.assertTrue('queuekey' not in self.the_input.input_state)
         self.assertTrue('queuestate' not in self.the_input.input_state)
-        test_system.xqueue['interface'].send_to_queue.return_value = (0, 'Success!')
 
     def test_ungraded_response_success(self):
         queuekey = 'abcd'
@@ -496,7 +495,7 @@ class MatlabTest(unittest.TestCase):
                  'feedback': {'message': '3'}, }
         elt = etree.fromstring(self.xml)
 
-        the_input = self.input_class(test_system, elt, state)
+        the_input = self.input_class(test_system(), elt, state)
         inner_msg = 'hello!'
         queue_msg = json.dumps({'msg': inner_msg})
 
@@ -514,7 +513,7 @@ class MatlabTest(unittest.TestCase):
                  'feedback': {'message': '3'}, }
         elt = etree.fromstring(self.xml)
 
-        the_input = self.input_class(test_system, elt, state)
+        the_input = self.input_class(test_system(), elt, state)
         inner_msg = 'hello!'
         queue_msg = json.dumps({'msg': inner_msg})
 
@@ -553,7 +552,7 @@ class SchematicTest(unittest.TestCase):
         state = {'value': value,
                  'status': 'unsubmitted'}
 
-        the_input = lookup_tag('schematic')(test_system, element, state)
+        the_input = lookup_tag('schematic')(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -592,7 +591,7 @@ class ImageInputTest(unittest.TestCase):
         state = {'value': value,
                  'status': 'unsubmitted'}
 
-        the_input = lookup_tag('imageinput')(test_system, element, state)
+        the_input = lookup_tag('imageinput')(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -643,7 +642,7 @@ class CrystallographyTest(unittest.TestCase):
         state = {'value': value,
                  'status': 'unsubmitted'}
 
-        the_input = lookup_tag('crystallography')(test_system, element, state)
+        the_input = lookup_tag('crystallography')(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -681,7 +680,7 @@ class VseprTest(unittest.TestCase):
         state = {'value': value,
                  'status': 'unsubmitted'}
 
-        the_input = lookup_tag('vsepr_input')(test_system, element, state)
+        the_input = lookup_tag('vsepr_input')(test_system(), element, state)
 
         context = the_input._get_render_context()
 
@@ -708,7 +707,7 @@ class ChemicalEquationTest(unittest.TestCase):
         element = etree.fromstring(xml_str)
 
         state = {'value': 'H2OYeah', }
-        self.the_input = lookup_tag('chemicalequationinput')(test_system, element, state)
+        self.the_input = lookup_tag('chemicalequationinput')(test_system(), element, state)
 
     def test_rendering(self):
         ''' Verify that the render context matches the expected render context'''
@@ -783,7 +782,7 @@ class DragAndDropTest(unittest.TestCase):
                                     ]
                     }
 
-        the_input = lookup_tag('drag_and_drop_input')(test_system, element, state)
+        the_input = lookup_tag('drag_and_drop_input')(test_system(), element, state)
 
         context = the_input._get_render_context()
         expected = {'id': 'prob_1_2',
@@ -832,7 +831,7 @@ class AnnotationInputTest(unittest.TestCase):
 
         tag = 'annotationinput'
 
-        the_input = lookup_tag(tag)(test_system, element, state)
+        the_input = lookup_tag(tag)(test_system(), element, state)
 
         context = the_input._get_render_context()
 
diff --git a/common/lib/xmodule/xmodule/tests/__init__.py b/common/lib/xmodule/xmodule/tests/__init__.py
index 79e1fec0f0..bcf333d7d9 100644
--- a/common/lib/xmodule/xmodule/tests/__init__.py
+++ b/common/lib/xmodule/xmodule/tests/__init__.py
@@ -33,15 +33,14 @@ def test_system():
     """
     Construct a test ModuleSystem instance.
 
-    By default, the render_template() method simply returns
-    the context it is passed as a string.
-    You can override this behavior by monkey patching:
+    By default, the render_template() method simply returns the context it is
+    passed as a string.  You can override this behavior by monkey patching::
 
-    system = test_system()
-    system.render_template = my_render_func
+        system = test_system()
+        system.render_template = my_render_func
+
+    where `my_render_func` is a function of the form my_render_func(template, context).
 
-    where my_render_func is a function of the form
-    my_render_func(template, context)
     """
     return ModuleSystem(
         ajax_url='courses/course_id/modx/a_location',