diff --git a/eslint.config.js b/eslint.config.js
index 65fa512..fff73c6 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -1,17 +1,33 @@
 import { defineConfig, globalIgnores } from "eslint/config";
+import globals from "globals";
 
 export default defineConfig([
   globalIgnores(["node"]),
   {
     files: ["tests/**/*.js"],
+    languageOptions: {
+      // Only allow ECMAScript built-ins and CTS harness globals.
+      // This causes no-undef to flag any runtime-specific API (setTimeout, process, Buffer, etc.).
+      globals: {
+        ...globals.es2025,
+        // CTS harness globals
+        assert: "readonly",
+        loadAddon: "readonly",
+        mustCall: "readonly",
+        mustNotCall: "readonly",
+        gcUntil: "readonly",
+        experimentalFeatures: "readonly",
+      },
+    },
     rules: {
-      // Test files are expected to be self-contained
+      "no-undef": "error",
       "no-restricted-imports": ["error", {
         patterns: ["*"],
       }],
-      "no-restricted-globals": ["error",
-        { name: "require", message: "Test files are expected to be self-contained" }
-      ]
+      "no-restricted-syntax": ["error",
+        { selector: "MemberExpression[object.name='globalThis']", message: "Avoid globalThis access in test files — use CTS harness globals instead" },
+        { selector: "MemberExpression[object.name='global']", message: "Avoid global access in test files — use CTS harness globals instead" }
+      ],
     },
   },
 ]);
diff --git a/package-lock.json b/package-lock.json
index d8ec84f..2f8e71a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -13,6 +13,7 @@
       "devDependencies": {
         "@types/node": "^24.10.1",
         "eslint": "^9.39.1",
+        "globals": "^17.4.0",
         "node-api-headers": "^1.7.0"
       }
     },
@@ -123,6 +124,19 @@
         "url": "https://opencollective.com/eslint"
       }
     },
+    "node_modules/@eslint/eslintrc/node_modules/globals": {
+      "version": "14.0.0",
+      "resolved": "https://registry.npmjs.org/globals/-/globals-14.0.0.tgz",
+      "integrity": "sha512-oahGvuMGQlPw/ivIYBjVSrWAfWLBeku5tpPE2fOPLi+WHffIWbuh2tCjhyQhTBPMf5E9jDEH4FOmTYgYwbKwtQ==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=18"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/sindresorhus"
+      }
+    },
     "node_modules/@eslint/eslintrc/node_modules/strip-json-comments": {
       "version": "3.1.1",
       "resolved": "https://registry.npmjs.org/strip-json-comments/-/strip-json-comments-3.1.1.tgz",
@@ -688,9 +702,9 @@
       }
     },
     "node_modules/globals": {
-      "version": "14.0.0",
-      "resolved": "https://registry.npmjs.org/globals/-/globals-14.0.0.tgz",
-      "integrity": "sha512-oahGvuMGQlPw/ivIYBjVSrWAfWLBeku5tpPE2fOPLi+WHffIWbuh2tCjhyQhTBPMf5E9jDEH4FOmTYgYwbKwtQ==",
+      "version": "17.4.0",
+      "resolved": "https://registry.npmjs.org/globals/-/globals-17.4.0.tgz",
+      "integrity": "sha512-hjrNztw/VajQwOLsMNT1cbJiH2muO3OROCHnbehc8eY5JyD2gqz4AcMHPqgaOR59DjgUjYAYLeH699g/eWi2jw==",
       "dev": true,
       "license": "MIT",
       "engines": {
diff --git a/package.json b/package.json
index 1590d7b..0288ad9 100644
--- a/package.json
+++ b/package.json
@@ -13,6 +13,7 @@
   "devDependencies": {
     "@types/node": "^24.10.1",
     "eslint": "^9.39.1",
+    "globals": "^17.4.0",
     "node-api-headers": "^1.7.0"
   },
   "dependencies": {