feat(test-utils): add CPU performance integration test harness (#24951)

packages/test-utils/src/env-setup.ts

@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { join } from 'node:path';
+
+/**
+ * Isolate the test environment by setting environment variables
+ * to point to a temporary run directory.
+ *
+ * @param runDir - The temporary directory for this test run.
+ */
+export function isolateTestEnv(runDir: string): void {
+  // Set the home directory to the test run directory to avoid conflicts
+  // with the user's local config.
+  process.env['HOME'] = runDir;
+  if (process.platform === 'win32') {
+    process.env['USERPROFILE'] = runDir;
+  }
+
+  // We also need to set the config dir explicitly, since the code might
+  // construct the path before the HOME env var is set.
+  process.env['GEMINI_CONFIG_DIR'] = join(runDir, '.gemini');
+
+  // Force file storage to avoid keychain prompts/hangs in CI, especially on macOS
+  process.env['GEMINI_FORCE_FILE_STORAGE'] = 'true';
+
+  // Mark as integration test
+  process.env['GEMINI_CLI_INTEGRATION_TEST'] = 'true';
+
+  // Isolate telemetry log
+  process.env['TELEMETRY_LOG_FILE'] = join(runDir, 'telemetry.log');
+}