Tests are now functional (only running without syntax errors) on Python 3 too.
diff --git a/tests/test_varblock.py b/tests/test_varblock.py
index d8addb4..6195258 100644
--- a/tests/test_varblock.py
+++ b/tests/test_varblock.py
@@ -1,6 +1,9 @@
 '''Tests varblock operations.'''
 
-from StringIO import StringIO
+try:
+    from StringIO import StringIO
+except ImportError:
+    from io import StringIO
 import unittest
 
 import rsa