Add google.auth._oauth2client - helpers for oauth2client migration (#70)

diff --git a/tests/test__oauth2client.py b/tests/test__oauth2client.py
new file mode 100644
index 0000000..9478406
--- /dev/null
+++ b/tests/test__oauth2client.py
@@ -0,0 +1,157 @@
+# Copyright 2016 Google Inc.
+#
+# 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 datetime
+import os
+import sys
+
+import mock
+import oauth2client.client
+import oauth2client.contrib.gce
+import oauth2client.service_account
+import pytest
+from six.moves import reload_module
+
+from google.auth import _oauth2client
+
+
+DATA_DIR = os.path.join(os.path.dirname(__file__), 'data')
+SERVICE_ACCOUNT_JSON_FILE = os.path.join(DATA_DIR, 'service_account.json')
+
+
+def test__convert_oauth2_credentials():
+    old_credentials = oauth2client.client.OAuth2Credentials(
+        'access_token', 'client_id', 'client_secret', 'refresh_token',
+        datetime.datetime.min, 'token_uri', 'user_agent', scopes='one two')
+
+    new_credentials = _oauth2client._convert_oauth2_credentials(
+        old_credentials)
+
+    assert new_credentials.token == old_credentials.access_token
+    assert new_credentials._refresh_token == old_credentials.refresh_token
+    assert new_credentials._client_id == old_credentials.client_id
+    assert new_credentials._client_secret == old_credentials.client_secret
+    assert new_credentials._token_uri == old_credentials.token_uri
+    assert new_credentials.scopes == old_credentials.scopes
+
+
+def test__convert_service_account_credentials():
+    old_class = oauth2client.service_account.ServiceAccountCredentials
+    old_credentials = old_class.from_json_keyfile_name(
+        SERVICE_ACCOUNT_JSON_FILE)
+
+    new_credentials = _oauth2client._convert_service_account_credentials(
+        old_credentials)
+
+    assert (new_credentials._service_account_email ==
+            old_credentials.service_account_email)
+    assert new_credentials._signer.key_id == old_credentials._private_key_id
+    assert new_credentials._token_uri == old_credentials.token_uri
+
+
+def test__convert_service_account_credentials_with_jwt():
+    old_class = oauth2client.service_account._JWTAccessCredentials
+    old_credentials = old_class.from_json_keyfile_name(
+        SERVICE_ACCOUNT_JSON_FILE)
+
+    new_credentials = _oauth2client._convert_service_account_credentials(
+        old_credentials)
+
+    assert (new_credentials._service_account_email ==
+            old_credentials.service_account_email)
+    assert new_credentials._signer.key_id == old_credentials._private_key_id
+    assert new_credentials._token_uri == old_credentials.token_uri
+
+
+def test__convert_gce_app_assertion_credentials():
+    old_credentials = oauth2client.contrib.gce.AppAssertionCredentials(
+        email='some_email')
+
+    new_credentials = _oauth2client._convert_gce_app_assertion_credentials(
+        old_credentials)
+
+    assert (new_credentials._service_account_email ==
+            old_credentials.service_account_email)
+
+
+@pytest.fixture
+def mock_oauth2client_gae_imports(mock_non_existent_module):
+    mock_non_existent_module('google.appengine.api.app_identity')
+    mock_non_existent_module('google.appengine.ext.ndb')
+    mock_non_existent_module('google.appengine.ext.webapp.util')
+    mock_non_existent_module('webapp2')
+
+
+@mock.patch('google.auth.app_engine.app_identity')
+def test__convert_appengine_app_assertion_credentials(
+        app_identity, mock_oauth2client_gae_imports):
+
+    import oauth2client.contrib.appengine
+
+    service_account_id = 'service_account_id'
+    old_credentials = oauth2client.contrib.appengine.AppAssertionCredentials(
+        scope='one two', service_account_id=service_account_id)
+
+    new_credentials = (
+        _oauth2client._convert_appengine_app_assertion_credentials(
+            old_credentials))
+
+    assert new_credentials.scopes == ['one', 'two']
+    assert (new_credentials._service_account_id ==
+            old_credentials.service_account_id)
+
+
+class MockCredentials(object):
+    pass
+
+
+def test_convert_success():
+    convert_function = mock.Mock()
+    conversion_map_patch = mock.patch.object(
+        _oauth2client, '_CLASS_CONVERSION_MAP',
+        {MockCredentials: convert_function})
+    credentials = MockCredentials()
+
+    with conversion_map_patch:
+        result = _oauth2client.convert(credentials)
+
+    convert_function.assert_called_once_with(credentials)
+    assert result == convert_function.return_value
+
+
+def test_convert_not_found():
+    with pytest.raises(ValueError) as excinfo:
+        _oauth2client.convert('a string is not a real credentials class')
+
+    assert excinfo.match('Unable to convert')
+
+
+@pytest.fixture
+def reset__oauth2client_module():
+    """Reloads the _oauth2client module after a test."""
+    reload_module(_oauth2client)
+
+
+def test_import_has_app_engine(
+        mock_oauth2client_gae_imports, reset__oauth2client_module):
+    reload_module(_oauth2client)
+    assert _oauth2client._HAS_APPENGINE
+
+
+def test_import_without_oauth2client(monkeypatch, reset__oauth2client_module):
+    monkeypatch.setitem(sys.modules, 'oauth2client', None)
+    with pytest.raises(ImportError) as excinfo:
+        reload_module(_oauth2client)
+
+    assert excinfo.match('oauth2client')