diff --git a/bigtable/google/cloud/bigtable/client.py b/bigtable/google/cloud/bigtable/client.py
index 86ee7173c917b..62877371a945a 100644
--- a/bigtable/google/cloud/bigtable/client.py
+++ b/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'
diff --git a/bigtable/tests/unit/test_client.py b/bigtable/tests/unit/test_client.py
index 17656be60c00d..c3ab8d1ed8887 100644
--- a/bigtable/tests/unit/test_client.py
+++ b/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):
diff --git a/core/google/cloud/client.py b/core/google/cloud/client.py
index 5906ab5ed1086..468cf9e40a526 100644
--- a/core/google/cloud/client.py
+++ b/core/google/cloud/client.py
@@ -21,9 +21,9 @@
 import google_auth_httplib2
 import six
 
+import google.auth
 import google.auth.credentials
 from google.cloud._helpers import _determine_default_project
-from google.cloud.credentials import get_credentials
 from google.oauth2 import service_account
 
 
@@ -135,7 +135,7 @@ def __init__(self, credentials=None, _http=None):
                     credentials, google.auth.credentials.Credentials)):
             raise ValueError(_GOOGLE_AUTH_CREDENTIALS_HELP)
         if credentials is None and _http is None:
-            credentials = get_credentials()
+            credentials, _ = google.auth.default()
         self._credentials = google.auth.credentials.with_scopes_if_required(
             credentials, self.SCOPE)
         self._http_internal = _http
diff --git a/core/google/cloud/credentials.py b/core/google/cloud/credentials.py
index 29c4a5d310f4f..f33d61144cb05 100644
--- a/core/google/cloud/credentials.py
+++ b/core/google/cloud/credentials.py
@@ -27,19 +27,6 @@
 from google.cloud._helpers import UTC
 
 
-def get_credentials():
-    """Gets credentials implicitly from the current environment.
-
-    Uses :func:`google.auth.default()`.
-
-    :rtype: :class:`google.auth.credentials.Credentials`,
-    :returns: A new credentials instance corresponding to the implicit
-              environment.
-    """
-    credentials, _ = google.auth.default()
-    return credentials
-
-
 def _get_signed_query_params(credentials, expiration, string_to_sign):
     """Gets query parameters for creating a signed URL.
 
diff --git a/core/nox.py b/core/nox.py
index 48b55332283ea..1dca10eb9b694 100644
--- a/core/nox.py
+++ b/core/nox.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 from __future__ import absolute_import
+import os
 
 import nox
 
@@ -29,16 +30,26 @@ def unit_tests(session, python_version):
     session.virtualenv_dirname = 'unit-' + python_version
 
     # Install all test dependencies, then install this package in-place.
-    session.install('mock', 'pytest', 'pytest-cov',
-                    'grpcio >= 1.0.2')
+    session.install(
+        'mock',
+        'pytest',
+        'pytest-cov',
+        'grpcio >= 1.0.2',
+    )
     session.install('-e', '.')
 
     # Run py.test against the unit tests.
     session.run(
-        'py.test', '--quiet',
-        '--cov=google.cloud', '--cov=tests.unit', '--cov-append',
-        '--cov-config=.coveragerc', '--cov-report=', '--cov-fail-under=97',
-        'tests/unit',
+        'py.test',
+        '--quiet',
+        '--cov=google.cloud',
+        '--cov=tests.unit',
+        '--cov-append',
+        '--cov-config=.coveragerc',
+        '--cov-report=',
+        '--cov-fail-under=97',
+        os.path.join('tests', 'unit'),
+        *session.posargs
     )
 
 
diff --git a/core/tests/unit/test_client.py b/core/tests/unit/test_client.py
index 14eac68abee32..25667712c69a9 100644
--- a/core/tests/unit/test_client.py
+++ b/core/tests/unit/test_client.py
@@ -59,37 +59,31 @@ def test_unpickleable(self):
         with self.assertRaises(pickle.PicklingError):
             pickle.dumps(client_obj)
 
-    def test_ctor_defaults(self):
-        from google.cloud._testing import _Monkey
-        from google.cloud import client
-
-        CREDENTIALS = _make_credentials()
-        FUNC_CALLS = []
-
-        def mock_get_credentials():
-            FUNC_CALLS.append('get_credentials')
-            return CREDENTIALS
+    def test_constructor_defaults(self):
+        credentials = _make_credentials()
 
-        with _Monkey(client, get_credentials=mock_get_credentials):
+        patch = mock.patch(
+            'google.auth.default', return_value=(credentials, None))
+        with patch as default:
             client_obj = self._make_one()
 
-        self.assertIs(client_obj._credentials, CREDENTIALS)
+        self.assertIs(client_obj._credentials, credentials)
         self.assertIsNone(client_obj._http_internal)
-        self.assertEqual(FUNC_CALLS, ['get_credentials'])
+        default.assert_called_once_with()
 
-    def test_ctor_explicit(self):
-        CREDENTIALS = _make_credentials()
-        HTTP = object()
-        client_obj = self._make_one(credentials=CREDENTIALS, _http=HTTP)
+    def test_constructor_explicit(self):
+        credentials = _make_credentials()
+        http = mock.sentinel.http
+        client_obj = self._make_one(credentials=credentials, _http=http)
 
-        self.assertIs(client_obj._credentials, CREDENTIALS)
-        self.assertIs(client_obj._http_internal, HTTP)
+        self.assertIs(client_obj._credentials, credentials)
+        self.assertIs(client_obj._http_internal, http)
 
-    def test_ctor_bad_credentials(self):
-        CREDENTIALS = object()
+    def test_constructor_bad_credentials(self):
+        credentials = mock.sentinel.credentials
 
         with self.assertRaises(ValueError):
-            self._make_one(credentials=CREDENTIALS)
+            self._make_one(credentials=credentials)
 
     def test_from_service_account_json(self):
         from google.cloud import _helpers
@@ -162,34 +156,27 @@ def _get_target_class():
     def _make_one(self, *args, **kw):
         return self._get_target_class()(*args, **kw)
 
-    def test_ctor_defaults(self):
-        from google.cloud._testing import _Monkey
-        from google.cloud import client
-
-        PROJECT = 'PROJECT'
-        CREDENTIALS = _make_credentials()
-        FUNC_CALLS = []
-
-        def mock_determine_proj(project):
-            FUNC_CALLS.append((project, '_determine_default_project'))
-            return PROJECT
+    def test_constructor_defaults(self):
+        credentials = _make_credentials()
+        patch1 = mock.patch(
+            'google.auth.default', return_value=(credentials, None))
 
-        def mock_get_credentials():
-            FUNC_CALLS.append('get_credentials')
-            return CREDENTIALS
+        project = 'prahj-ekt'
+        patch2 = mock.patch(
+            'google.cloud.client._determine_default_project',
+            return_value=project)
 
-        with _Monkey(client, get_credentials=mock_get_credentials,
-                     _determine_default_project=mock_determine_proj):
-            client_obj = self._make_one()
+        with patch1 as default:
+            with patch2 as _determine_default_project:
+                client_obj = self._make_one()
 
-        self.assertEqual(client_obj.project, PROJECT)
-        self.assertIs(client_obj._credentials, CREDENTIALS)
+        self.assertEqual(client_obj.project, project)
+        self.assertIs(client_obj._credentials, credentials)
         self.assertIsNone(client_obj._http_internal)
-        self.assertEqual(
-            FUNC_CALLS,
-            [(None, '_determine_default_project'), 'get_credentials'])
+        default.assert_called_once_with()
+        _determine_default_project.assert_called_once_with(None)
 
-    def test_ctor_missing_project(self):
+    def test_constructor_missing_project(self):
         from google.cloud._testing import _Monkey
         from google.cloud import client
 
@@ -204,7 +191,7 @@ def mock_determine_proj(project):
 
         self.assertEqual(FUNC_CALLS, [(None, '_determine_default_project')])
 
-    def test_ctor_w_invalid_project(self):
+    def test_constructor_w_invalid_project(self):
         CREDENTIALS = _make_credentials()
         HTTP = object()
         with self.assertRaises(ValueError):
@@ -227,11 +214,11 @@ def _explicit_ctor_helper(self, project):
         self.assertIs(client_obj._credentials, CREDENTIALS)
         self.assertIs(client_obj._http_internal, HTTP)
 
-    def test_ctor_explicit_bytes(self):
+    def test_constructor_explicit_bytes(self):
         PROJECT = b'PROJECT'
         self._explicit_ctor_helper(PROJECT)
 
-    def test_ctor_explicit_unicode(self):
+    def test_constructor_explicit_unicode(self):
         PROJECT = u'PROJECT'
         self._explicit_ctor_helper(PROJECT)
 
diff --git a/core/tests/unit/test_credentials.py b/core/tests/unit/test_credentials.py
index aaffa907dda1c..bcc969c9db5de 100644
--- a/core/tests/unit/test_credentials.py
+++ b/core/tests/unit/test_credentials.py
@@ -12,29 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import base64
+import calendar
+import datetime
+import time
 import unittest
 
 import mock
 import six
 
 
-class Test_get_credentials(unittest.TestCase):
-
-    def _call_fut(self):
-        from google.cloud import credentials
-
-        return credentials.get_credentials()
-
-    def test_it(self):
-        with mock.patch('google.auth.default', autospec=True) as default:
-            default.return_value = (
-                mock.sentinel.credentials, mock.sentinel.project)
-            found = self._call_fut()
-
-        self.assertIs(found, mock.sentinel.credentials)
-        default.assert_called_once_with()
-
-
 class Test_generate_signed_url(unittest.TestCase):
 
     def _call_fut(self, *args, **kwargs):
@@ -44,7 +31,6 @@ def _call_fut(self, *args, **kwargs):
 
     def _generate_helper(self, response_type=None, response_disposition=None,
                          generation=None):
-        import base64
         from six.moves.urllib.parse import parse_qs
         from six.moves.urllib.parse import urlsplit
         import google.auth.credentials
@@ -108,7 +94,6 @@ def test_w_custom_fields(self):
 
 class Test_generate_signed_url_exception(unittest.TestCase):
     def test_with_google_credentials(self):
-        import time
         import google.auth.credentials
         from google.cloud.credentials import generate_signed_url
 
@@ -129,7 +114,6 @@ def _call_fut(self, credentials, expiration, string_to_sign):
                                         string_to_sign)
 
     def test_it(self):
-        import base64
         import google.auth.credentials
 
         SIG_BYTES = b'DEADBEEF'
@@ -158,8 +142,6 @@ def _call_fut(self, expiration):
         return _get_expiration_seconds(expiration)
 
     def _utc_seconds(self, when):
-        import calendar
-
         return int(calendar.timegm(when.timetuple()))
 
     def test_w_invalid(self):
@@ -176,14 +158,11 @@ def test_w_long(self):
         self.assertEqual(self._call_fut(long(123)), 123)  # noqa: F821
 
     def test_w_naive_datetime(self):
-        import datetime
-
         expiration_no_tz = datetime.datetime(2004, 8, 19, 0, 0, 0, 0)
         utc_seconds = self._utc_seconds(expiration_no_tz)
         self.assertEqual(self._call_fut(expiration_no_tz), utc_seconds)
 
     def test_w_utc_datetime(self):
-        import datetime
         from google.cloud._helpers import UTC
 
         expiration_utc = datetime.datetime(2004, 8, 19, 0, 0, 0, 0, UTC)
@@ -191,7 +170,6 @@ def test_w_utc_datetime(self):
         self.assertEqual(self._call_fut(expiration_utc), utc_seconds)
 
     def test_w_other_zone_datetime(self):
-        import datetime
         from google.cloud._helpers import _UTC
 
         class CET(_UTC):
@@ -205,7 +183,6 @@ class CET(_UTC):
         self.assertEqual(self._call_fut(expiration_other), cet_seconds)
 
     def test_w_timedelta_seconds(self):
-        import datetime
         from google.cloud._testing import _Monkey
         from google.cloud import credentials as MUT
 
@@ -219,7 +196,6 @@ def test_w_timedelta_seconds(self):
         self.assertEqual(result, utc_seconds + 10)
 
     def test_w_timedelta_days(self):
-        import datetime
         from google.cloud._testing import _Monkey
         from google.cloud import credentials as MUT
 
diff --git a/datastore/nox.py b/datastore/nox.py
index 2cf2186aa45a0..f93b02944631b 100644
--- a/datastore/nox.py
+++ b/datastore/nox.py
@@ -38,10 +38,17 @@ def unit_tests(session, python_version):
     session.install('-e', '.')
 
     # Run py.test against the unit tests.
-    session.run('py.test', '--quiet',
-        '--cov=google.cloud.datastore', '--cov=tests.unit', '--cov-append',
-        '--cov-config=.coveragerc', '--cov-report=', '--cov-fail-under=97',
-        'tests/unit',
+    session.run(
+        'py.test',
+        '--quiet',
+        '--cov=google.cloud.datastore',
+        '--cov=tests.unit',
+        '--cov-append',
+        '--cov-config=.coveragerc',
+        '--cov-report=',
+        '--cov-fail-under=97',
+        os.path.join('tests', 'unit'),
+        *session.posargs
     )
 
 
diff --git a/datastore/tests/unit/test_client.py b/datastore/tests/unit/test_client.py
index 9824e06b73ad0..a03bbe8b710fc 100644
--- a/datastore/tests/unit/test_client.py
+++ b/datastore/tests/unit/test_client.py
@@ -148,22 +148,16 @@ def test_constructor_w_implicit_inputs(self):
 
         other = 'other'
         creds = _make_credentials()
-        default_called = []
-
-        def fallback_mock(project):
-            default_called.append(project)
-            return project or other
 
         klass = self._get_target_class()
         patch1 = mock.patch(
             'google.cloud.datastore.client._determine_default_project',
-            new=fallback_mock)
+            return_value=other)
         patch2 = mock.patch(
-            'google.cloud.client.get_credentials',
-            return_value=creds)
+            'google.auth.default', return_value=(creds, None))
 
-        with patch1:
-            with patch2:
+        with patch1 as _determine_default_project:
+            with patch2 as default:
                 client = klass()
 
         self.assertEqual(client.project, other)
@@ -174,7 +168,9 @@ def fallback_mock(project):
 
         self.assertIsNone(client.current_batch)
         self.assertIsNone(client.current_transaction)
-        self.assertEqual(default_called, [None])
+
+        default.assert_called_once_with()
+        _determine_default_project.assert_called_once_with(None)
 
     def test_constructor_w_explicit_inputs(self):
         from google.cloud.datastore.client import _DATASTORE_BASE_URL
diff --git a/datastore/tests/unit/test_query.py b/datastore/tests/unit/test_query.py
index b361ec25a42fa..26c1b6cc0831d 100644
--- a/datastore/tests/unit/test_query.py
+++ b/datastore/tests/unit/test_query.py
@@ -550,21 +550,14 @@ def _call_fut(self, iterator, entity_pb):
         return _item_to_entity(iterator, entity_pb)
 
     def test_it(self):
-        from google.cloud._testing import _Monkey
-        from google.cloud.datastore import helpers
-
-        result = object()
-        entities = []
-
-        def mocked(entity_pb):
-            entities.append(entity_pb)
-            return result
-
-        entity_pb = object()
-        with _Monkey(helpers, entity_from_protobuf=mocked):
-            self.assertIs(result, self._call_fut(None, entity_pb))
-
-        self.assertEqual(entities, [entity_pb])
+        entity_pb = mock.sentinel.entity_pb
+        patch = mock.patch(
+            'google.cloud.datastore.helpers.entity_from_protobuf')
+        with patch as entity_from_protobuf:
+            result = self._call_fut(None, entity_pb)
+            self.assertIs(result, entity_from_protobuf.return_value)
+
+        entity_from_protobuf.assert_called_once_with(entity_pb)
 
 
 class Test__pb_from_query(unittest.TestCase):
diff --git a/spanner/google/cloud/spanner/client.py b/spanner/google/cloud/spanner/client.py
index 875238aed2bc2..b701b017abb03 100644
--- a/spanner/google/cloud/spanner/client.py
+++ b/spanner/google/cloud/spanner/client.py
@@ -24,6 +24,7 @@
   :class:`~google.cloud.spanner.database.Database`
 """
 
+import google.auth
 import google.auth.credentials
 from google.gax import INITIAL_PAGE
 # pylint: disable=line-too-long
@@ -36,7 +37,6 @@
 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.iterator import GAXIterator
 from google.cloud.spanner import __version__
 from google.cloud.spanner._helpers import _options_with_prefix
@@ -109,7 +109,7 @@ def __init__(self, project=None, credentials=None,
 
         _ClientProjectMixin.__init__(self, project=project)
         if credentials is None:
-            credentials = get_credentials()
+            credentials, _ = google.auth.default()
 
         scopes = [
             SPANNER_ADMIN_SCOPE,
diff --git a/spanner/tests/unit/test_client.py b/spanner/tests/unit/test_client.py
index c71429c225352..e5e90fd6b7ab1 100644
--- a/spanner/tests/unit/test_client.py
+++ b/spanner/tests/unit/test_client.py
@@ -88,19 +88,17 @@ def test_constructor_custom_user_agent_and_timeout(self):
                                       user_agent=CUSTOM_USER_AGENT)
 
     def test_constructor_implicit_credentials(self):
-        from google.cloud._testing import _Monkey
-        from google.cloud.spanner import client as MUT
-
         creds = _make_credentials()
 
-        def mock_get_credentials():
-            return creds
-
-        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()
+
     def test_constructor_credentials_wo_create_scoped(self):
         creds = _make_credentials()
         expected_scopes = None