tests: add centralized VPCSC config detection (#9581)

See:
https://docs.google.com/document/d/1qCRRNqzKn7YnssbB1g-RTkJH11S3vmJ97JjsLWo6alA

Toward #9580.

test_utils/test_utils/vpcsc_config.py

@@ -0,0 +1,118 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright 2019 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
+#
+#     https://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
+
+import pytest
+
+
+INSIDE_VPCSC_ENVVAR = "GOOGLE_CLOUD_TESTS_IN_VPCSC"
+PROJECT_INSIDE_ENVVAR = "PROJECT_ID"
+PROJECT_OUTSIDE_ENVVAR = "GOOGLE_CLOUD_TESTS_VPCSC_OUTSIDE_PERIMETER_PROJECT"
+BUCKET_OUTSIDE_ENVVVAR = "GOOGLE_CLOUD_TESTS_VPCSC_OUTSIDE_PERIMETER_BUCKET"
+
+
+class VPCSCTestConfig(object):
+    """System test utility for VPCSC detection.
+
+    See: https://cloud.google.com/vpc-service-controls/docs/
+    """
+
+    @property
+    def inside_vpcsc(self):
+        """Test whether the test environment is configured to run inside VPCSC.
+
+        Returns:
+            bool:
+                true if the environment is configured to run inside VPCSC,
+                else false.
+        """
+        return INSIDE_VPCSC_ENVVAR in os.environ
+
+    @property
+    def project_inside(self):
+        """Project ID for testing outside access.
+
+        Returns:
+            str: project ID used for testing outside access; None if undefined.
+        """
+        return os.environ.get(PROJECT_INSIDE_ENVVAR, None)
+
+    @property
+    def project_outside(self):
+        """Project ID for testing inside access.
+
+        Returns:
+            str: project ID used for testing inside access; None if undefined.
+        """
+        return os.environ.get(PROJECT_OUTSIDE_ENVVAR, None)
+
+    @property
+    def bucket_outside(self):
+        """GCS bucket for testing inside access.
+
+        Returns:
+            str: bucket ID used for testing inside access; None if undefined.
+        """
+        return os.environ.get(BUCKET_OUTSIDE_ENVVAR, None)
+
+    def skip_if_inside_vpcsc(self, testcase):
+        """Test decorator: skip if running inside VPCSC."""
+        reason = (
+            "Running inside VPCSC.  "
+            "Set the {} environment variable to enable this test."
+        ).format(INSIDE_VPCSC_ENVVAR)
+        skip = pytest.mark.skipif(self.inside_vpcsc, reason=reason)
+        return skip(testcase)
+
+    def skip_unless_inside_vpcsc(self, testcase):
+        """Test decorator: skip if running outside VPCSC."""
+        reason = (
+            "Running outside VPCSC.  "
+            "Unset the {} environment variable to enable this test."
+        ).format(INSIDE_VPCSC_ENVVAR)
+        skip = pytest.mark.skipif(not self.inside_vpcsc, reason=reason)
+        return skip(testcase)
+
+    def skip_unless_inside_project(self, testcase):
+        """Test decorator: skip if inside project env var not set."""
+        reason = (
+            "Project ID for running inside VPCSC not set.  "
+            "Set the {} environment variable to enable this test."
+        ).format(PROJECT_INSIDE_ENVVAR)
+        skip = pytest.mark.skipif(self.project_inside is None, reason=reason)
+        return skip(testcase)
+
+    def skip_unless_outside_project(self, testcase):
+        """Test decorator: skip if outside project env var not set."""
+        reason = (
+            "Project ID for running outside VPCSC not set. "
+            "Set the {} environment variable to enable this test."
+        ).format(PROJECT_OUTSIDE_ENVVAR)
+        skip = pytest.mark.skipif(self.project_outside is None, reason=reason)
+        return skip(testcase)
+
+    def skip_unless_outside_bucket(self, testcase):
+        """Test decorator: skip if outside bucket env var not set."""
+        reason = (
+            "Bucket ID for running outside VPCSC not set. "
+            "Set the {} environment variable to enable this test."
+        ).format(BUCKET_OUTSIDE_ENVVAR)
+        skip = pytest.mark.skipif(self.bucket_outside is None, reason=reason)
+        return skip(testcase)
+
+
+vpcsc_config = VPCSCTestConfig()