fix: isolate unit tests from workstation mTLS environments and fix core_deps_from_source in noxfile

Author: hebaalazzeh

packages/google-api-core/noxfile.py

@@ -350,7 +350,7 @@ def prerelease_deps(session):
 @nox.session(python=DEFAULT_PYTHON_VERSION)
 def core_deps_from_source(session):
     """Run the test suite installing dependencies from source."""
-    default(session, prerelease=True)
+    default(session, install_deps_from_source=True)
 
 
 @nox.session(python=DEFAULT_PYTHON_VERSION)

packages/google-api-core/tests/conftest.py

@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+# Copyright 2026 Google LLC
+#
+# 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 os
+from unittest import mock
+import pytest
+
+
+@pytest.fixture(scope="session", autouse=True)
+def mock_mtls_env():
+    """Autouse session-scoped fixture to isolate unit tests from workstation mTLS environments."""
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield