diff --git a/pdfrw/pdfwriter.py b/pdfrw/pdfwriter.py
index 789527c..cb884cb 100755
--- a/pdfrw/pdfwriter.py
+++ b/pdfrw/pdfwriter.py
@@ -138,7 +138,7 @@ def format_obj(obj):
                     if compress and obj.stream:
                         do_compress([obj])
                     pairs = sorted((getattr(x, 'encoded', None) or x, y)
-                                   for (x, y) in obj.iteritems())
+                                   for (x, y) in iteritems(obj))
                     myarray = []
                     for key, value in pairs:
                         myarray.append(key)
diff --git a/tests/test_examples.py b/tests/test_examples.py
index 6871b80..aac2d00 100755
--- a/tests/test_examples.py
+++ b/tests/test_examples.py
@@ -94,7 +94,7 @@ def do_test(self, params, prev_results=[''], scrub=False):
                     os.remove(dstf)
                 if scrub and os.path.exists(scrub):
                     os.remove(scrub)
-                subprocess.call(params)
+                subprocess.check_output(params)
                 if scrub:
                     PdfWriter(dstf).addpages(PdfReader(scrub).pages).write()
             with open(dstf, 'rb') as f:
@@ -109,7 +109,7 @@ def do_test(self, params, prev_results=[''], scrub=False):
             if expects:
                 if len(expects) == 1:
                     expects, = expects
-                    self.assertEqual(hash, expects)
+                    self.assertEqual(hash, expects, '{} file does not have the expected MD5 hash'.format(dstf))
                 else:
                     self.assertIn(hash, expects)
                 result = 'pass'
diff --git a/tests/test_roundtrip.py b/tests/test_roundtrip.py
index 2e097b6..62bdcc9 100755
--- a/tests/test_roundtrip.py
+++ b/tests/test_roundtrip.py
@@ -91,7 +91,7 @@ def roundtrip(self, testname, basename, srcf, decompress=False,
             if expects:
                 if len(expects) == 1:
                     expects, = expects
-                    self.assertEqual(hash, expects)
+                    self.assertEqual(hash, expects, '{} file does not have the expected MD5 hash'.format(dstf))
                 else:
                     self.assertIn(hash, expects)
                 result = 'pass'