Only run migration state test in 1.7 or greater

setup.py

@@ -27,7 +27,8 @@
         'Programming Language :: Python :: 3.3',
         "License :: OSI Approved :: BSD License",
     ],
-    tests_require=["Django>=1.4", "webtest==2.0.6", "django-webtest==1.7"],
+    tests_require=["Django>=1.4", "webtest==2.0.6", "django-webtest==1.7",
+                   "unittest2"],
     include_package_data=True,
     test_suite='runtests.main',
 )

simple_history/tests/tests/test_models.py

@@ -1,14 +1,15 @@
 from __future__ import unicode_literals
 
 from datetime import datetime, timedelta
+from unittest2 import skipUnless
 
+import django
 try:
     from django.contrib.auth import get_user_model
     User = get_user_model()
 except ImportError:  # django 1.4 compatibility
     from django.contrib.auth.models import User
 from django.db.models.loading import get_model
-from django.db.migrations import state
 from django.test import TestCase
 from django.core.files.base import ContentFile
 
@@ -471,5 +472,7 @@ def test_string_related(self):
         field_object = HistoricalState._meta.get_field_by_name('library_id')[0]
         self.assertEqual(field_object.related.model, State)
 
+    @skipUnless(django.get_version() >= "1.7", "Requires 1.7 migrations")
     def test_state_serialization_of_customfk(self):
+        from django.db.migrations import state
         state.ModelState.from_model(HistoricalCustomFKError)