diff --git a/CHANGES b/CHANGES
index 9c75f144..5ea2baae 100644
--- a/CHANGES
+++ b/CHANGES
@@ -8,6 +8,9 @@ Version 1.0
 
 (release date to be announced, codename to be selected)
 
+- Added `**kwargs` to :meth:`flask.Test.test_client` to support passing
+  additional keyword arguments to the constructor of
+  :attr:`flask.Flask.test_client_class`.
 - Added ``SESSION_REFRESH_EACH_REQUEST`` config key that controls the
   set-cookie behavior.  If set to `True` a permanent session will be
   refreshed each request and get their lifetime extended, if set to
@@ -20,8 +23,8 @@ Version 1.0
 - Added :meth:`flask.Config.from_json`.
 - Added :attr:`flask.Flask.config_class`.
 - Added :meth:`flask.config.Config.get_namespace`.
-- Added ``TEMPLATES_AUTO_RELOAD`` config key. If disabled the 
-  templates will be reloaded only if the application is running in 
+- Added ``TEMPLATES_AUTO_RELOAD`` config key. If disabled the
+  templates will be reloaded only if the application is running in
   debug mode. For higher performance it’s possible to disable that.
 - Added a workaround for a limitation in Python 3.3's namespace loader.
 - Added support for explicit root paths when using Python 3.3's namespace
diff --git a/flask/app.py b/flask/app.py
index 2840f426..4e97605e 100644
--- a/flask/app.py
+++ b/flask/app.py
@@ -821,7 +821,7 @@ class Flask(_PackageBoundObject):
             # without reloader and that stuff from an interactive shell.
             self._got_first_request = False
 
-    def test_client(self, use_cookies=True):
+    def test_client(self, use_cookies=True, **kwargs):
         """Creates a test client for this application.  For information
         about unit testing head over to :ref:`testing`.
 
@@ -844,6 +844,20 @@ class Flask(_PackageBoundObject):
                 rv = c.get('/?vodka=42')
                 assert request.args['vodka'] == '42'
 
+        Additionally, you may pass optional keyword arguments that will then
+        be passed to the application's :attr:`test_client_class` constructor.
+        For example::
+
+            from flask.testing import FlaskClient
+
+            class CustomClient(FlaskClient):
+                def __init__(self, authentication=None, *args, **kwargs):
+                    FlaskClient.__init__(*args, **kwargs)
+                    self._authentication = authentication
+
+            app.test_client_class = CustomClient
+            client = app.test_client(authentication='Basic ....')
+
         See :class:`~flask.testing.FlaskClient` for more information.
 
         .. versionchanged:: 0.4
@@ -853,11 +867,15 @@ class Flask(_PackageBoundObject):
            The `use_cookies` parameter was added as well as the ability
            to override the client to be used by setting the
            :attr:`test_client_class` attribute.
+
+        .. versionchanged:: 1.0
+           Added `**kwargs` to support passing additional keyword arguments to
+           the constructor of :attr:`test_client_class`.
         """
         cls = self.test_client_class
         if cls is None:
             from flask.testing import FlaskClient as cls
-        return cls(self, self.response_class, use_cookies=use_cookies)
+        return cls(self, self.response_class, use_cookies=use_cookies, **kwargs)
 
     def open_session(self, request):
         """Creates or opens a new session.  Default implementation stores all