diff --git a/google/auth/_default.py b/google/auth/_default.py
index cedd8a99a..8dd8ac3b0 100644
--- a/google/auth/_default.py
+++ b/google/auth/_default.py
@@ -112,7 +112,9 @@ def _get_gae_credentials():
 
 
 def _get_gce_credentials():
-    if _metadata.ping():
+    # TODO: Ping now requires a request argument. Figure out how to deal with
+    # that.
+    if _metadata.ping(request=None):
         return compute_engine.Credentials()
 
 
diff --git a/google/auth/compute_engine/_metadata.py b/google/auth/compute_engine/_metadata.py
index 8768adfa6..4c0104a8c 100644
--- a/google/auth/compute_engine/_metadata.py
+++ b/google/auth/compute_engine/_metadata.py
@@ -25,7 +25,7 @@
 from six.moves.urllib import parse as urlparse
 
 from google.auth import _helpers
-from google.auth import transport
+from google.auth import exceptions
 
 _METADATA_ROOT = 'http://metadata.google.internal/computeMetadata/v1/'
 
@@ -42,10 +42,12 @@
     _METADATA_DEFAULT_TIMEOUT = 3
 
 
-def ping(timeout=_METADATA_DEFAULT_TIMEOUT):
+def ping(request, timeout=_METADATA_DEFAULT_TIMEOUT):
     """Checks to see if the metadata server is available.
 
     Args:
+        request (google.auth.transport.Request): A callable used to make
+            HTTP requests.
         timeout (int): How long to wait for the metadata server to respond.
 
     Returns:
@@ -58,8 +60,8 @@ def ping(timeout=_METADATA_DEFAULT_TIMEOUT):
     #       the metadata resolution was particularly slow. The latter case is
     #       "unlikely".
     try:
-        response = transport.request(
-            None, 'GET', _METADATA_IP_ROOT, headers=_METADATA_HEADERS,
+        response = request(
+            'GET', _METADATA_IP_ROOT, headers=_METADATA_HEADERS,
             timeout=timeout, retries=False)
         return response.status == http_client.OK
 
@@ -70,11 +72,12 @@ def ping(timeout=_METADATA_DEFAULT_TIMEOUT):
         return False
 
 
-def get(http, path, root=_METADATA_ROOT, recursive=None):
+def get(request, path, root=_METADATA_ROOT, recursive=None):
     """Fetch a resource from the metadata server.
 
     Args:
-        http (Any): The transport HTTP object.
+        request (google.auth.transport.Request): A callable used to make
+            HTTP requests.
         path (str): The resource to retrieve. For example,
             ``'instance/service-accounts/defualt'``.
         root (str): The full path to the metadata server root.
@@ -88,13 +91,13 @@ def get(http, path, root=_METADATA_ROOT, recursive=None):
             returned as a string.
 
     Raises:
-        http_client.HTTPException: if an error occurred while retrieving
-            metadata.
+        google.auth.exceptions.TransportError: if an error occurred while
+            retrieving metadata.
     """
     url = urlparse.urljoin(root, path)
     url = _helpers.update_query(url, {'recursive': recursive})
 
-    response = transport.request(http, 'GET', url, headers=_METADATA_HEADERS)
+    response = request('GET', url, headers=_METADATA_HEADERS)
 
     if response.status == http_client.OK:
         content = _helpers.from_bytes(response.data)
@@ -103,17 +106,18 @@ def get(http, path, root=_METADATA_ROOT, recursive=None):
         else:
             return content
     else:
-        raise http_client.HTTPException(
+        raise exceptions.TransportError(
             'Failed to retrieve {} from the Google Compute Engine'
             'metadata service. Status: {} Response:\n{}'.format(
-                url, response.status, response.data))
+                url, response.status, response.data), response)
 
 
-def get_service_account_info(http, service_account='default'):
+def get_service_account_info(request, service_account='default'):
     """Get information about a service account from the metadata server.
 
     Args:
-        http (Any): The transport HTTP object.
+        request (google.auth.transport.Request): A callable used to make
+            HTTP requests.
         service_account (str): The string 'default' or a service account email
             address. The determines which service account for which to acquire
             information.
@@ -128,20 +132,21 @@ def get_service_account_info(http, service_account='default'):
             }
 
     Raises:
-        http_client.HTTPException: if an error occurred while retrieving
-            metadata.
+        google.auth.exceptions.TransportError: if an error occurred while
+            retrieving metadata.
     """
     return get(
-        http,
+        request,
         'instance/service-accounts/{0}/'.format(service_account),
         recursive=True)
 
 
-def get_service_account_token(http, service_account='default'):
+def get_service_account_token(request, service_account='default'):
     """Get the OAuth 2.0 access token for a service account.
 
     Args:
-        http (Any): The transport HTTP object.
+        request (google.auth.transport.Request): A callable used to make
+            HTTP requests.
         service_account (str): The string 'default' or a service account email
             address. The determines which service account for which to acquire
             an access token.
@@ -150,11 +155,11 @@ def get_service_account_token(http, service_account='default'):
         Union[str, datetime]: The access token and its expiration.
 
     Raises:
-        http_client.HTTPException: if an error occurred while retrieving
-            metadata.
+        google.auth.exceptions.TransportError: if an error occurred while
+            retrieving metadata.
     """
     token_json = get(
-        http,
+        request,
         'instance/service-accounts/{0}/token'.format(service_account))
     token_expiry = _helpers.now() + datetime.timedelta(
         seconds=token_json['expires_in'])
diff --git a/google/auth/credentials.py b/google/auth/credentials.py
index d001665d8..c28fb0c16 100644
--- a/google/auth/credentials.py
+++ b/google/auth/credentials.py
@@ -72,11 +72,12 @@ def expired(self):
             return True
 
     @abc.abstractmethod
-    def refresh(self, http):
+    def refresh(self, request):
         """Refreshes the access token.
 
         Args:
-            http (Any): The transport http object.
+            request (google.auth.transport.Request): A callable used to make
+                HTTP requests.
 
         Raises:
             google.auth.exceptions.RefreshError: If the credentials could
@@ -97,14 +98,15 @@ def apply(self, headers, token=None):
         headers[b'authorization'] = 'Bearer {}'.format(
             _helpers.from_bytes(token or self.token))
 
-    def before_request(self, http, method, url, headers):
+    def before_request(self, request, method, url, headers):
         """Performs credential-specific before request logic.
 
         Refreshes the credentials if necessary, then calls :meth:`apply` to
         apply the token to the authentication header.
 
         Args:
-            http (Any): The transport HTTP object.
+            request (google.auth.transport.Request): A callable used to make
+                HTTP requests.
             method (str): The request's HTTP method.
             url (str): The request's URI.
             headers (Mapping): The request's headers.
@@ -113,7 +115,7 @@ def before_request(self, http, method, url, headers):
         # (Subclasses may use these arguments to ascertain information about
         # the http request.)
         if not self.valid:
-            self.refresh(http)
+            self.refresh(request)
         self.apply(headers)
 
 
diff --git a/google/auth/exceptions.py b/google/auth/exceptions.py
index 6ce029557..de6266c71 100644
--- a/google/auth/exceptions.py
+++ b/google/auth/exceptions.py
@@ -20,6 +20,11 @@ class GoogleAuthError(Exception):
     pass
 
 
+class TransportError(Exception):
+    """Used to indicate an error occurred during an HTTP request."""
+    pass
+
+
 class RefreshError(GoogleAuthError):
     """Used to indicate that an error occurred while refreshing the
     credentials' access token."""
diff --git a/google/auth/jwt.py b/google/auth/jwt.py
index a6d9438e5..5fdc6e5fe 100644
--- a/google/auth/jwt.py
+++ b/google/auth/jwt.py
@@ -392,11 +392,11 @@ def _make_one_time_jwt(self, uri):
         token, _ = self._make_jwt(audience=audience)
         return token
 
-    def refresh(self, http):
+    def refresh(self, request):
         """Refreshes the access token.
 
         Args:
-            http (Any): The transport http object.
+            request (Any): Unused.
         """
         # pylint: disable=unused-argument
         # (pylint doens't correctly recognize overriden methods.)
@@ -414,7 +414,7 @@ def sign_bytes(self, message):
         """
         return self._signer.sign(message)
 
-    def before_request(self, http, method, url, headers):
+    def before_request(self, request, method, url, headers):
         """Performs credential-specific before request logic.
 
         If an audience is specified it will refresh the credentials if
@@ -423,7 +423,7 @@ def before_request(self, http, method, url, headers):
         authorization header in headers to the token.
 
         Args:
-            http (Any): The transport http object.
+            request (Any): Unused.
             method (str): The request's HTTP method.
             url (str): The request's URI.
             headers (Mapping): The request's headers.
@@ -435,7 +435,7 @@ def before_request(self, http, method, url, headers):
         # there is a valid token and apply the auth headers.
         if self._audience:
             if not self.valid:
-                self.refresh(http)
+                self.refresh(request)
             self.apply(headers)
         # Otherwise, generate a one-time token using the URL
         # (without the query string and fragement) as the audience.
diff --git a/google/auth/service_account.py b/google/auth/service_account.py
index 6a80c4921..70243810a 100644
--- a/google/auth/service_account.py
+++ b/google/auth/service_account.py
@@ -81,7 +81,6 @@
 from google.auth import credentials
 from google.auth import exceptions
 from google.auth import jwt
-from google.auth import transport
 
 _DEFAULT_TOKEN_LIFETIME_SECS = 3600  # 1 hour in sections
 _JWT_TOKEN_GRANT_TYPE = 'urn:ietf:params:oauth:grant-type:jwt-bearer'
@@ -257,7 +256,7 @@ def _make_authorization_grant_assertion(self):
         return token
 
     @_helpers.copy_docstring(credentials.Credentials)
-    def refresh(self, http):
+    def refresh(self, request):
         assertion = self._make_authorization_grant_assertion()
 
         body = urllib.parse.urlencode({
@@ -269,9 +268,8 @@ def refresh(self, http):
             'content-type': 'application/x-www-form-urlencoded',
         }
 
-        response = transport.request(
-            http, method='POST', url=self._token_uri, headers=headers,
-            body=body)
+        response = request(
+            url=self._token_uri, method='POST', headers=headers, body=body)
 
         if response.status != http_client.OK:
             # Try to decode the response and extract details.
diff --git a/google/auth/transport.py b/google/auth/transport.py
deleted file mode 100644
index c5976fc5e..000000000
--- a/google/auth/transport.py
+++ /dev/null
@@ -1,29 +0,0 @@
-# Copyright 2016 Google Inc. All rights reserved.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-"""Temporary tansport module."""
-
-import urllib3
-
-
-def _default_http():
-    return urllib3.PoolManager()
-
-
-def request(http, *args, **kwargs):
-    """Make a request using the transport."""
-    if http is None:
-        http = _default_http()
-
-    return http.request(*args, **kwargs)
diff --git a/google/auth/transport/__init__.py b/google/auth/transport/__init__.py
new file mode 100644
index 000000000..e43147a77
--- /dev/null
+++ b/google/auth/transport/__init__.py
@@ -0,0 +1,82 @@
+# Copyright 2016 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Transport - HTTP client library support.
+
+:mod:`google.auth` is designed to work with various HTTP client libraries such
+as urllib3 and requests. In order to work across these libraries with different
+interfaces some abstraction is needed.
+
+This module provides two interfaces that are implemented by transport adapters
+to support HTTP libraries. :class:`Request` defines the interface expected by
+:mod:`google.auth` to make requests. :class:`Response` defines the interface
+for the return value of :class:`Request`.
+"""
+
+import abc
+
+import six
+
+
+@six.add_metaclass(abc.ABCMeta)
+class Response(object):
+    """HTTP Response data."""
+
+    @abc.abstractproperty
+    def status(self):
+        """int: The HTTP status code."""
+
+    @abc.abstractproperty
+    def headers(self):
+        """Mapping: The HTTP response headers."""
+
+    @abc.abstractproperty
+    def data(self):
+        """bytes: The response body."""
+
+
+@six.add_metaclass(abc.ABCMeta)
+class Request(object):
+    """Interface for a callable that makes HTTP requests.
+
+    Specific transport implementations should provide an implementation of
+    this that adapts their specific request / response API.
+    """
+
+    @abc.abstractmethod
+    def __call__(self, url, method='GET', body=None, headers=None,
+                 timeout=None, **kwargs):
+        """Make an HTTP request.
+
+        Args:
+            url (str): The URI to be requested.
+            method (str): The HTTP method to use for the request. Defaults
+                to 'GET'.
+            body (bytes): The payload / body in HTTP request.
+            headers (Mapping): Request headers.
+            timeout (Optional(int)): The number of seconds to wait for a
+                response from the server. If not specified or if None, the
+                transport-specific default timeout will be used.
+            kwargs: Additionally arguments passed on to the transport's
+                request method.
+
+        Returns:
+            Response: The HTTP response.
+
+        Raises:
+            google.auth.exceptions.TransportError: If any exception occurred.
+        """
+        # pylint: disable=redundant-returns-doc, missing-raises-doc
+        # (pylint doesn't play well with abstract docstrings.)
+        raise NotImplementedError('__call__ must be implemented.')
diff --git a/google/auth/transport/urllib3.py b/google/auth/transport/urllib3.py
new file mode 100644
index 000000000..51d8af499
--- /dev/null
+++ b/google/auth/transport/urllib3.py
@@ -0,0 +1,67 @@
+# Copyright 2016 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Transport adapter for urllib3."""
+
+from __future__ import absolute_import
+
+import urllib3
+import urllib3.exceptions
+
+from google.auth import exceptions
+from google.auth import transport
+
+
+class Request(transport.Request):
+    """Urllib3 request adapter
+
+    Args:
+        http (urllib3.requests.RequestMethods): An instance of any urllib3
+            class that implements :cls:`~urllib3.requests.RequestMethods`,
+            usually :cls:`urllib3.PoolManager`.
+    """
+    def __init__(self, http):
+        self.http = http
+
+    def __call__(self, url, method='GET', body=None, headers=None,
+                 timeout=None, **kwargs):
+        """
+        Args:
+            url (str): The URI to be requested.
+            method (str): The HTTP method to use for the request. Defaults
+                to 'GET'.
+            body (bytes): The payload / body in HTTP request.
+            headers (Mapping): Request headers.
+            timeout (Optional(int)): The number of seconds to wait for a
+                response from the server. If not specified or if None, the
+                urllib3 default timeout will be used.
+            kwargs: Additional arguments passed throught to the underlying
+                urllib3 :meth:`urlopen` method.
+
+        Returns:
+            Response: The HTTP response.
+
+        Raises:
+            google.auth.exceptions.TransportError: If any exception occurred.
+        """
+        # Urllib3 uses a sentinel default value for timeout, so only set it if
+        # specified.
+        if timeout is not None:
+            kwargs['timeout'] = timeout
+
+        try:
+            return self.http.request(
+                method, url, body=body, headers=headers, **kwargs)
+        except urllib3.exceptions.HTTPError as exc:
+            raise exceptions.TransportError(exc)
diff --git a/tests/compute_engine/test__metadata.py b/tests/compute_engine/test__metadata.py
index 24964de69..2b49feee8 100644
--- a/tests/compute_engine/test__metadata.py
+++ b/tests/compute_engine/test__metadata.py
@@ -20,32 +20,33 @@
 from six.moves import http_client
 
 from google.auth import _helpers
+from google.auth import exceptions
 from google.auth.compute_engine import _metadata
 
-HTTP_OBJECT = mock.Mock()
 PATH = 'instance/service-accounts/default'
 
 
 @pytest.fixture
 def mock_request():
-    with mock.patch('google.auth.transport.request') as request_mock:
-        def set_response(data, status=http_client.OK, headers=None):
-            response = mock.Mock()
-            response.status = status
-            response.data = _helpers.to_bytes(data)
-            response.headers = headers or {}
-            request_mock.return_value = response
-            return request_mock
-        yield set_response
+    request_mock = mock.Mock()
+
+    def set_response(data, status=http_client.OK, headers=None):
+        response = mock.Mock()
+        response.status = status
+        response.data = _helpers.to_bytes(data)
+        response.headers = headers or {}
+        request_mock.return_value = response
+        return request_mock
+
+    yield set_response
 
 
 def test_ping_success(mock_request):
     request_mock = mock_request('')
 
-    assert _metadata.ping()
+    assert _metadata.ping(request_mock)
 
     request_mock.assert_called_once_with(
-        None,
         'GET',
         _metadata._METADATA_IP_ROOT,
         headers=_metadata._METADATA_HEADERS,
@@ -57,7 +58,7 @@ def test_ping_failure(mock_request):
     request_mock = mock_request('')
     request_mock.side_effect = Exception()
 
-    assert not _metadata.ping()
+    assert not _metadata.ping(request_mock)
 
 
 def test_get_success_json(mock_request):
@@ -65,10 +66,9 @@ def test_get_success_json(mock_request):
     request_mock = mock_request(
         data, headers={'content-type': 'application/json'})
 
-    result = _metadata.get(HTTP_OBJECT, PATH)
+    result = _metadata.get(request_mock, PATH)
 
     request_mock.assert_called_once_with(
-        HTTP_OBJECT,
         'GET',
         _metadata._METADATA_ROOT + PATH,
         headers=_metadata._METADATA_HEADERS)
@@ -79,10 +79,9 @@ def test_get_success_text(mock_request):
     data = 'foobar'
     request_mock = mock_request(data, headers={'content-type': 'text/plain'})
 
-    result = _metadata.get(HTTP_OBJECT, PATH)
+    result = _metadata.get(request_mock, PATH)
 
     request_mock.assert_called_once_with(
-        HTTP_OBJECT,
         'GET',
         _metadata._METADATA_ROOT + PATH,
         headers=_metadata._METADATA_HEADERS)
@@ -93,13 +92,12 @@ def test_get_failure(mock_request):
     request_mock = mock_request(
         'Metadata error', status=http_client.NOT_FOUND)
 
-    with pytest.raises(http_client.HTTPException) as excinfo:
-        _metadata.get(HTTP_OBJECT, PATH)
+    with pytest.raises(exceptions.TransportError) as excinfo:
+        _metadata.get(request_mock, PATH)
 
     assert excinfo.match(r'Metadata error')
 
     request_mock.assert_called_once_with(
-        HTTP_OBJECT,
         'GET',
         _metadata._METADATA_ROOT + PATH,
         headers=_metadata._METADATA_HEADERS)
@@ -111,10 +109,9 @@ def test_get_service_account_token(now, mock_request):
         json.dumps({'access_token': 'token', 'expires_in': 500}),
         headers={'content-type': 'application/json'})
 
-    token, expiry = _metadata.get_service_account_token(HTTP_OBJECT)
+    token, expiry = _metadata.get_service_account_token(request_mock)
 
     request_mock.assert_called_once_with(
-        HTTP_OBJECT,
         'GET',
         _metadata._METADATA_ROOT + PATH + '/token',
         headers=_metadata._METADATA_HEADERS)
@@ -127,10 +124,9 @@ def test_get_service_account_info(mock_request):
         json.dumps({'foo': 'bar'}),
         headers={'content-type': 'application/json'})
 
-    info = _metadata.get_service_account_info(HTTP_OBJECT)
+    info = _metadata.get_service_account_info(request_mock)
 
     request_mock.assert_called_once_with(
-        HTTP_OBJECT,
         'GET',
         _metadata._METADATA_ROOT + PATH + '/?recursive=True',
         headers=_metadata._METADATA_HEADERS)
diff --git a/tests/test_service_account.py b/tests/test_service_account.py
index 7e328d3c4..bfa6d9e6e 100644
--- a/tests/test_service_account.py
+++ b/tests/test_service_account.py
@@ -159,18 +159,17 @@ def test__make_authorization_grant_assertion_subject(self):
         payload = jwt.decode(token, PUBLIC_CERT_BYTES)
         assert payload['sub'] == 'user@example.com'
 
-    @mock.patch('google.auth.transport.request')
-    def test_refresh_success(self, request_mock):
+    def test_refresh_success(self):
         response = mock.Mock()
         response.status = http_client.OK
         response.data = json.dumps({
             'access_token': 'token',
             'expires_in': 500
         }).encode('utf-8')
-        request_mock.return_value = response
+        request_mock = mock.Mock(return_value=response)
 
         # Refresh credentials
-        self.credentials.refresh(None)
+        self.credentials.refresh(request_mock)
 
         # Check request data
         assert request_mock.called
@@ -191,49 +190,46 @@ def test_refresh_success(self, request_mock):
         # expired)
         assert self.credentials.valid
 
-    @mock.patch('google.auth.transport.request')
-    def test_refresh_error(self, request_mock):
+    def test_refresh_error(self):
         response = mock.Mock()
         response.status = http_client.BAD_REQUEST
         response.data = json.dumps({
             'error': 'error',
             'error_description': 'error description'
         }).encode('utf-8')
-        request_mock.return_value = response
+        request_mock = mock.Mock(return_value=response)
 
         with pytest.raises(exceptions.RefreshError) as excinfo:
-            self.credentials.refresh(None)
+            self.credentials.refresh(request_mock)
 
         assert excinfo.match(r'error: error description')
 
-    @mock.patch('google.auth.transport.request')
-    def test_refresh_error_non_json(self, request_mock):
+    def test_refresh_error_non_json(self):
         response = mock.Mock()
         response.status = http_client.BAD_REQUEST
         response.data = 'non-json error'.encode('utf-8')
-        request_mock.return_value = response
+        request_mock = mock.Mock(return_value=response)
 
         with pytest.raises(exceptions.RefreshError) as excinfo:
-            self.credentials.refresh(None)
+            self.credentials.refresh(request_mock)
 
         assert excinfo.match(r'non-json error')
 
-    @mock.patch('google.auth.transport.request')
-    def test_before_request_refreshes(self, request_mock):
+    def test_before_request_refreshes(self):
         response = mock.Mock()
         response.status = http_client.OK
         response.data = json.dumps({
             'access_token': 'token',
             'expires_in': 500
         }).encode('utf-8')
-        request_mock.return_value = response
+        request_mock = mock.Mock(return_value=response)
 
         # Credentials should start as invalid
         assert not self.credentials.valid
 
         # before_request should cause a refresh
         self.credentials.before_request(
-            mock.Mock(), 'GET', 'http://example.com?a=1#3', {})
+            request_mock, 'GET', 'http://example.com?a=1#3', {})
 
         # The refresh endpoint should've been called.
         assert request_mock.called
diff --git a/tests/test_transport.py b/tests/test_transport.py
deleted file mode 100644
index 72f29c0b2..000000000
--- a/tests/test_transport.py
+++ /dev/null
@@ -1,39 +0,0 @@
-# Copyright 2016 Google Inc. All rights reserved.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-import mock
-import urllib3
-
-from google.auth import transport
-
-
-def test__default_http():
-    http = transport._default_http()
-    assert isinstance(http, urllib3.PoolManager)
-
-
-def test_request():
-    http = mock.Mock()
-    transport.request(http, 'a', b='c')
-    http.request.assert_called_with('a', b='c')
-
-
-@mock.patch('google.auth.transport._default_http')
-def test_request_no_http(default_http_mock):
-    http_mock = mock.Mock()
-    default_http_mock.return_value = http_mock
-
-    transport.request(None, 'a', b='c')
-
-    http_mock.request.assert_called_with('a', b='c')