dropped support for Python3.1 due to problems with unittest2py3k test discovery

tests/test_common.py

@@ -40,7 +40,7 @@ class TestSearchExact(unittest.TestCase):
         return list(search_exact(sequence, subsequence))
 
     def test_bytes(self):
-        text = 'abc'
+        text = b'abc'
         self.assertEqual(self.search(text, text), [0])
 
     def test_unicode(self):

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py26, py27, py31, py32, py33
+envlist = py26, py27, py32, py33
 
 [testenv]
 commands = python setup.py test
@@ -22,32 +22,25 @@ deps =
     {[testenv]deps}
     biopython
 
-[testenv:py31]
-changedir = {toxworkdir}
-commands =
-    2to3 -n -W --output-dir {envtmpdir}/tests3/tests {toxinidir}/tests
-    {envpython} -m unittest2 discover {envtmpdir}/tests3/tests
-    rm -rf {envtmpdir}/tests3
-deps =
-    unittest2py3k
-    mock
-    {[testenv]deps}
-
 [testenv:py32]
+setenv =
+    PYTHONPATH = {envtmpdir}/tests3
 changedir = {toxworkdir}
 commands =
     2to3 -n -W --output-dir {envtmpdir}/tests3/tests {toxinidir}/tests
-    {envpython} -m unittest discover {envtmpdir}/tests3/tests
+    {envpython} -m unittest discover {envtmpdir}/tests3
     rm -rf {envtmpdir}/tests3
 deps =
     mock
     {[testenv]deps}
 
 [testenv:py33]
+setenv =
+    PYTHONPATH = {envtmpdir}/tests3
 changedir = {toxworkdir}
 commands =
     2to3 -n -W --output-dir {envtmpdir}/tests3/tests {toxinidir}/tests
-    {envpython} -m unittest discover {envtmpdir}/tests3/tests
+    {envpython} -m unittest discover {envtmpdir}/tests3
     rm -rf {envtmpdir}/tests3
 deps =
     {[testenv]deps}