diff --git a/tests/setns_test.py b/tests/setns_test.py
new file mode 100644
index 00000000..b8a75788
--- /dev/null
+++ b/tests/setns_test.py
@@ -0,0 +1,38 @@
+
+import os
+import socket
+
+import mitogen
+import mitogen.parent
+
+import unittest2
+
+import testlib
+
+
+class DockerTest(testlib.DockerMixin, testlib.TestCase):
+    def test_okay(self):
+        # Magic calls must happen as root.
+        try:
+            root = self.router.sudo()
+        except mitogen.core.StreamError:
+            raise unittest2.SkipTest("requires sudo to localhost root")
+
+        via_ssh = self.docker_ssh(
+            username='mitogen__has_sudo',
+            password='has_sudo_password',
+        )
+
+        via_setns = self.router.setns(
+            kind='docker',
+            container=self.dockerized_ssh.container_name,
+            via=root,
+        )
+
+        self.assertEquals(
+            via_ssh.call(socket.gethostname),
+            via_setns.call(socket.gethostname),
+        )
+
+if __name__ == '__main__':
+    unittest2.main()