tests for new establish_key wormhole hook

defered should behave similarly to the `verify` hook

src/wormhole/test/test_wormhole.py

@@ -522,6 +522,32 @@ class Basic(unittest.TestCase):
         self.assertEqual(len(pieces), 3) # nameplate plus two words
         self.assert_(re.search(r'^\d+-\w+-\w+$', code), code)
 
+    def _test_establish_key_hook(self, established):
+
+        timing = DebugTiming()
+        w = wormhole._Wormhole(APPID, "relay_url", reactor, None, timing)
+
+        if established is True:
+            w._key = b"key"
+        elif established is False:
+            w._key = None
+        else:
+            w._key = b"key"
+            w._error = WelcomeError()
+
+        d = w.establish_key()
+
+        if w._key is not None and established is True:
+            self.successResultOf(d)
+        elif established is False:
+            self.assertNot(d.called)
+        else:
+            self.failureResultOf(d)
+
+    def test_establish_key_hook(self):
+        for established in (True, False, "error"):
+            self._test_establish_key_hook(established)
+
     # make sure verify() can be called both before and after the verifier is
     # computed