Honor validated registration usernames

identity-provisioner/tests/test_provisioner.py

@@ -19,6 +19,13 @@ class ProvisionerTests(unittest.TestCase):
     def test_username_is_stable_and_sanitized(self):
         self.assertEqual("bernd.worsch", _username("Bernd.Worsch@binky-hedgehog.com"))
 
+    def test_preferred_username_is_honored_and_validated(self):
+        self.assertEqual("chosen.name", _username("other@example.test", "Chosen.Name"))
+        with self.assertRaisesRegex(ValueError, "invalid"):
+            _username("other@example.test", "not allowed!")
+        with self.assertRaisesRegex(ValueError, "reserved"):
+            _username("other@example.test", "admin")
+
     def test_dispatch_requires_idempotency(self):
         with self.assertRaisesRegex(ValueError, "idempotency_key"):
             dispatch(Fake(), "/v1/identities/suspend", {