Add compute engine metadata client (#11)

diff --git a/tests/compute_engine/__init__.py b/tests/compute_engine/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/compute_engine/__init__.py
diff --git a/tests/compute_engine/test__metadata.py b/tests/compute_engine/test__metadata.py
new file mode 100644
index 0000000..4cc3e55
--- /dev/null
+++ b/tests/compute_engine/test__metadata.py
@@ -0,0 +1,159 @@
+# 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 json
+
+import mock
+import pytest
+from six.moves import http_client
+
+from google.auth import _helpers
+from google.auth import exceptions
+from google.auth.compute_engine import _metadata
+
+PATH = 'instance/service-accounts/default'
+
+
+@pytest.fixture
+def mock_request():
+    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('', headers=_metadata._METADATA_HEADERS)
+
+    assert _metadata.ping(request_mock)
+
+    request_mock.assert_called_once_with(
+        method='GET',
+        url=_metadata._METADATA_IP_ROOT,
+        headers=_metadata._METADATA_HEADERS,
+        timeout=_metadata._METADATA_DEFAULT_TIMEOUT)
+
+
+def test_ping_failure_bad_flavor(mock_request):
+    request_mock = mock_request(
+        '', headers={_metadata._METADATA_FLAVOR_HEADER: 'meep'})
+
+    assert not _metadata.ping(request_mock)
+
+
+def test_ping_failure_connection_failed(mock_request):
+    request_mock = mock_request('')
+    request_mock.side_effect = exceptions.TransportError()
+
+    assert not _metadata.ping(request_mock)
+
+
+def test_get_success_json(mock_request):
+    key, value = 'foo', 'bar'
+
+    data = json.dumps({key: value})
+    request_mock = mock_request(
+        data, headers={'content-type': 'application/json'})
+
+    result = _metadata.get(request_mock, PATH)
+
+    request_mock.assert_called_once_with(
+        method='GET',
+        url=_metadata._METADATA_ROOT + PATH,
+        headers=_metadata._METADATA_HEADERS)
+    assert result[key] == value
+
+
+def test_get_success_text(mock_request):
+    data = 'foobar'
+    request_mock = mock_request(data, headers={'content-type': 'text/plain'})
+
+    result = _metadata.get(request_mock, PATH)
+
+    request_mock.assert_called_once_with(
+        method='GET',
+        url=_metadata._METADATA_ROOT + PATH,
+        headers=_metadata._METADATA_HEADERS)
+    assert result == data
+
+
+def test_get_failure(mock_request):
+    request_mock = mock_request(
+        'Metadata error', status=http_client.NOT_FOUND)
+
+    with pytest.raises(exceptions.TransportError) as excinfo:
+        _metadata.get(request_mock, PATH)
+
+    assert excinfo.match(r'Metadata error')
+
+    request_mock.assert_called_once_with(
+        method='GET',
+        url=_metadata._METADATA_ROOT + PATH,
+        headers=_metadata._METADATA_HEADERS)
+
+
+def test_get_failure_bad_json(mock_request):
+    request_mock = mock_request(
+        '{', headers={'content-type': 'application/json'})
+
+    with pytest.raises(exceptions.TransportError) as excinfo:
+        _metadata.get(request_mock, PATH)
+
+    assert excinfo.match(r'invalid JSON')
+
+    request_mock.assert_called_once_with(
+        method='GET',
+        url=_metadata._METADATA_ROOT + PATH,
+        headers=_metadata._METADATA_HEADERS)
+
+
+@mock.patch('google.auth._helpers.utcnow', return_value=datetime.datetime.min)
+def test_get_service_account_token(utcnow, mock_request):
+    ttl = 500
+    request_mock = mock_request(
+        json.dumps({'access_token': 'token', 'expires_in': ttl}),
+        headers={'content-type': 'application/json'})
+
+    token, expiry = _metadata.get_service_account_token(request_mock)
+
+    request_mock.assert_called_once_with(
+        method='GET',
+        url=_metadata._METADATA_ROOT + PATH + '/token',
+        headers=_metadata._METADATA_HEADERS)
+    assert token == 'token'
+    assert expiry == utcnow() + datetime.timedelta(seconds=ttl)
+
+
+def test_get_service_account_info(mock_request):
+    key, value = 'foo', 'bar'
+    request_mock = mock_request(
+        json.dumps({key: value}),
+        headers={'content-type': 'application/json'})
+
+    info = _metadata.get_service_account_info(request_mock)
+
+    request_mock.assert_called_once_with(
+        method='GET',
+        url=_metadata._METADATA_ROOT + PATH + '/?recursive=true',
+        headers=_metadata._METADATA_HEADERS)
+
+    assert info[key] == value
diff --git a/tests/test__helpers.py b/tests/test__helpers.py
index c2bc4a7..d475fc4 100644
--- a/tests/test__helpers.py
+++ b/tests/test__helpers.py
@@ -15,6 +15,7 @@
 import datetime
 
 import pytest
+from six.moves import urllib
 
 from google.auth import _helpers
 
@@ -60,3 +61,35 @@
 def test_from_bytes_with_nonstring_type():
     with pytest.raises(ValueError):
         _helpers.from_bytes(object())
+
+
+def _assert_query(url, expected):
+    parts = urllib.parse.urlsplit(url)
+    query = urllib.parse.parse_qs(parts.query)
+    assert query == expected
+
+
+def test_update_query_params_no_params():
+    uri = 'http://www.google.com'
+    updated = _helpers.update_query(uri, {'a': 'b'})
+    assert updated == uri + '?a=b'
+
+
+def test_update_query_existing_params():
+    uri = 'http://www.google.com?x=y'
+    updated = _helpers.update_query(uri, {'a': 'b', 'c': 'd&'})
+    _assert_query(updated, {'x': ['y'], 'a': ['b'], 'c': ['d&']})
+
+
+def test_update_query_replace_param():
+    base_uri = 'http://www.google.com'
+    uri = base_uri + '?x=a'
+    updated = _helpers.update_query(uri, {'x': 'b', 'y': 'c'})
+    _assert_query(updated, {'x': ['b'], 'y': ['c']})
+
+
+def test_update_query_remove_param():
+    base_uri = 'http://www.google.com'
+    uri = base_uri + '?x=a'
+    updated = _helpers.update_query(uri, {'y': 'c'}, remove=['x'])
+    _assert_query(updated, {'y': ['c']})