wormhole.py: add debug switch to enable dilation (for tests)

src/wormhole/wormhole.py

@@ -125,7 +125,7 @@ class _DelegatedWormhole(object):
 
 @implementer(IWormhole, IDeferredWormhole)
 class _DeferredWormhole(object):
-    def __init__(self, reactor, eq):
+    def __init__(self, reactor, eq, _enable_dilate=False):
         self._reactor = reactor
         self._welcome_observer = OneShotObserver(eq)
         self._code_observer = OneShotObserver(eq)
@@ -137,6 +137,8 @@ class _DeferredWormhole(object):
         self._closed = False
         self._closed_observer = OneShotObserver(eq)
 
+        self._enable_dilate = _enable_dilate
+
     def _set_boss(self, boss):
         self._boss = boss
 
@@ -192,7 +194,8 @@ class _DeferredWormhole(object):
         return derive_key(self._key, to_bytes(purpose), length)
 
     def dilate(self):
-        raise NotImplementedError
+        if not self._enable_dilate:
+            raise NotImplementedError
         return self._boss.dilate()  # fires with (endpoints)
 
     def close(self):
@@ -261,7 +264,8 @@ def create(
         tor=None,
         timing=None,
         stderr=sys.stderr,
-        _eventual_queue=None):
+        _eventual_queue=None,
+        _enable_dilate=False):
     timing = timing or DebugTiming()
     side = bytes_to_hexstr(os.urandom(5))
     journal = journal or ImmediateJournal()
@@ -270,13 +274,14 @@ def create(
     if delegate:
         w = _DelegatedWormhole(delegate)
     else:
-        w = _DeferredWormhole(reactor, eq)
+        w = _DeferredWormhole(reactor, eq, _enable_dilate=_enable_dilate)
     # this indicates Wormhole capabilities
     wormhole_versions = {
         "can-dilate": DILATION_VERSIONS,
         "dilation-abilities": Connector.get_connection_abilities(),
     }
-    wormhole_versions = {} # don't advertise Dilation yet: not ready
+    if not _enable_dilate:
+        wormhole_versions = {} # don't advertise Dilation yet: not ready
     wormhole_versions["app_versions"] = versions  # app-specific capabilities
     v = __version__
     if isinstance(v, type(b"")):