diff --git a/common/lib/codejail/codejail/tests/test_safe_exec.py b/common/lib/codejail/codejail/tests/test_safe_exec.py
new file mode 100644
index 0000000000..685e2b8c39
--- /dev/null
+++ b/common/lib/codejail/codejail/tests/test_safe_exec.py
@@ -0,0 +1,53 @@
+"""Test safe_exec.py"""
+
+import textwrap
+import unittest
+from nose.plugins.skip import SkipTest
+
+from codejail.safe_exec import safe_exec, not_safe_exec
+
+dedent = textwrap.dedent
+
+class SafeExecTests(object):
+    """The tests for `safe_exec`, will be mixed into specific test classes below."""
+    def test_set_values(self):
+        g, l = {}, {}
+        self.safe_exec("a = 17", g, l)
+        self.assertEqual(l['a'], 17)
+
+    def test_division(self):
+        g, l = {}, {}
+        # No future division: 1/2 is 0.
+        self.safe_exec("a = 1/2", g, l)
+        self.assertEqual(l['a'], 0)
+        # Future division: 1/2 is 0.5.
+        self.safe_exec("a = 1/2", g, l, future_division=True)
+        self.assertEqual(l['a'], 0.5)
+
+    def test_assumed_imports(self):
+        g, l = {}, {}
+        # Using string without importing it is bad.
+        with self.assertRaises(Exception):
+            self.safe_exec("a = string.ascii_lowercase[0]", g, l)
+        # Using string with an assumed import is fine.
+        self.safe_exec("a = string.ascii_lowercase[0]", g, l, assumed_imports=["string"])
+        self.assertEqual(l['a'], 'a')
+        # Can also import with a shorthand.
+        self.safe_exec("a = op.join('x', 'y')", g, l, assumed_imports=[("op", "os.path")])
+        self.assertEqual(l['a'][0], 'x')
+        self.assertEqual(l['a'][-1], 'y')
+
+
+class TestSafeExec(SafeExecTests, unittest.TestCase):
+    """Run SafeExecTests, with the real safe_exec."""
+    def safe_exec(self, *args, **kwargs):
+        safe_exec(*args, **kwargs)
+
+class TestNotSafeExec(SafeExecTests, unittest.TestCase):
+    """Run SafeExecTests, with not_safe_exec."""
+    def setUp(self):
+        if safe_exec is not_safe_exec:
+            raise SkipTest
+
+    def safe_exec(self, *args, **kwargs):
+        not_safe_exec(*args, **kwargs)