🎉Source Google Search Console: increase unit test coverage at least 90% (#13037)

* Added unitetsts and updated docs

* Fix typo

* Increased to 90

airbyte-integrations/connectors/source-google-search-console/unit_tests/conftest.py

@@ -0,0 +1,24 @@
+#
+# Copyright (c) 2021 Airbyte, Inc., all rights reserved.
+#
+
+from pytest import fixture
+
+
+@fixture(name="config")
+def config_fixture(requests_mock):
+    url = "https://oauth2.googleapis.com/token"
+    requests_mock.post(url, json={"access_token": "token", "expires_in": 10})
+    config = {
+        "site_urls": ["https://example.com"],
+        "start_date": "start_date",
+        "end_date": "end_date",
+        "authorization": {
+            "auth_type": "Client",
+            "client_id": "client_id",
+            "client_secret": "client_secret",
+            "refresh_token": "refresh_token"
+        }
+    }
+
+    return config