Removing get_credentials() from core. (#3667)

* Removing `get_credentials()` from `core`.

In the process also:

- Slight re-org on `nox.py` config (to pass posargs) for `core`
  and `datastore`
- Getting rid of last usage of `_Monkey` in datastore

This is part of `@jonparrott`'s effort to slim down / stabilize
`core`.

* Removing `google.cloud.credentials` module from docs.

Author: dhermes

packages/google-cloud-bigtable/google/cloud/bigtable/client.py

@@ -31,6 +31,7 @@
 
 import os
 
+import google.auth
 import google.auth.credentials
 from google.gax.utils import metrics
 from google.longrunning import operations_grpc
@@ -40,7 +41,6 @@
 from google.cloud._http import DEFAULT_USER_AGENT
 from google.cloud.client import _ClientFactoryMixin
 from google.cloud.client import _ClientProjectMixin
-from google.cloud.credentials import get_credentials
 from google.cloud.environment_vars import BIGTABLE_EMULATOR
 
 from google.cloud.bigtable import __version__
@@ -211,7 +211,7 @@ def __init__(self, project=None, credentials=None,
                  read_only=False, admin=False, user_agent=DEFAULT_USER_AGENT):
         _ClientProjectMixin.__init__(self, project=project)
         if credentials is None:
-            credentials = get_credentials()
+            credentials, _ = google.auth.default()
 
         if read_only and admin:
             raise ValueError('A read-only client cannot also perform'

packages/google-cloud-bigtable/tests/unit/test_client.py

@@ -360,20 +360,19 @@ def test_constructor_both_admin_and_read_only(self):
                                           read_only=True)
 
     def test_constructor_implicit_credentials(self):
-        from google.cloud._testing import _Monkey
-        from google.cloud.bigtable import client as MUT
+        from google.cloud.bigtable.client import DATA_SCOPE
 
         creds = _make_credentials()
-        expected_scopes = [MUT.DATA_SCOPE]
-
-        def mock_get_credentials():
-            return creds
+        expected_scopes = [DATA_SCOPE]
 
-        with _Monkey(MUT, get_credentials=mock_get_credentials):
+        patch = mock.patch(
+            'google.auth.default', return_value=(creds, None))
+        with patch as default:
             self._constructor_test_helper(
                 None, None,
                 expected_creds=creds.with_scopes.return_value)
 
+        default.assert_called_once_with()
         creds.with_scopes.assert_called_once_with(expected_scopes)
 
     def test_constructor_credentials_wo_create_scoped(self):