Google DNS: Mock API discovery to run tests without internet connection. (#5791)

* Google DNS: Mock API discovery to run tests without internet connection.

* Allow test to pass when run from main cerbot package.

certbot-dns-google/certbot_dns_google/dns_google.py

@@ -81,7 +81,7 @@ class _GoogleClient(object):
     Encapsulates all communication with the Google Cloud DNS API.
     """
 
-    def __init__(self, account_json=None):
+    def __init__(self, account_json=None, dns_api=None):
 
         scopes = ['https://www.googleapis.com/auth/ndev.clouddns.readwrite']
         if account_json is not None:
@@ -92,7 +92,12 @@ class _GoogleClient(object):
             credentials = None
             self.project_id = self.get_project_id()
 
-        self.dns = discovery.build('dns', 'v1', credentials=credentials, cache_discovery=False)
+        if not dns_api:
+            self.dns = discovery.build('dns', 'v1',
+                                       credentials=credentials,
+                                       cache_discovery=False)
+        else:
+            self.dns = dns_api
 
     def add_txt_record(self, domain, record_name, record_content, record_ttl):
         """

certbot-dns-google/certbot_dns_google/dns_google_test.py

@@ -4,7 +4,9 @@ import os
 import unittest
 
 import mock
+from googleapiclient import discovery
 from googleapiclient.errors import Error
+from googleapiclient.http import HttpMock
 from httplib2 import ServerNotFoundError
 
 from certbot import errors
@@ -68,7 +70,13 @@ class GoogleClientTest(unittest.TestCase):
     def _setUp_client_with_mock(self, zone_request_side_effect):
         from certbot_dns_google.dns_google import _GoogleClient
 
-        client = _GoogleClient(ACCOUNT_JSON_PATH)
+        pwd = os.path.dirname(__file__)
+        rel_path = 'testdata/discovery.json'
+        discovery_file = os.path.join(pwd, rel_path)
+        http_mock = HttpMock(discovery_file, {'status': '200'})
+        dns_api = discovery.build('dns', 'v1', http=http_mock)
+
+        client = _GoogleClient(ACCOUNT_JSON_PATH, dns_api)
 
         # Setup
         mock_mz = mock.MagicMock()