diff --git a/packages/testtools/package.json b/packages/testtools/package.json
index c845e37aa..a4cba9a2a 100644
--- a/packages/testtools/package.json
+++ b/packages/testtools/package.json
@@ -55,7 +55,8 @@
     },
     "peerDependencies": {
         "better-sqlite3": "catalog:",
-        "pg": "catalog:"
+        "pg": "catalog:",
+        "vitest": "^4.0.14"
     },
     "devDependencies": {
         "@types/better-sqlite3": "catalog:",
@@ -65,7 +66,8 @@
         "@zenstackhq/eslint-config": "workspace:*",
         "@zenstackhq/tsdown-config": "workspace:*",
         "@zenstackhq/typescript-config": "workspace:*",
-        "typescript": "catalog:"
+        "typescript": "catalog:",
+        "vitest": "^4.0.14"
     },
     "funding": "https://github.com/sponsors/zenstackhq"
 }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 8f9f69741..9d153c351 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1020,6 +1020,9 @@ importers:
       typescript:
         specifier: 'catalog:'
         version: 6.0.3
+      vitest:
+        specifier: ^4.0.14
+        version: 4.0.14(@edge-runtime/vm@5.0.0)(@types/node@20.19.24)(happy-dom@20.8.9)(jiti@2.7.0)(jsdom@27.1.0)(lightningcss@1.30.2)(terser@5.44.0)(tsx@4.22.4)(yaml@2.9.0)
 
   packages/zod:
     dependencies:
diff --git a/tests/regression/test/issue-2659.test.ts b/tests/regression/test/issue-2659.test.ts
new file mode 100644
index 000000000..ef03d6bcd
--- /dev/null
+++ b/tests/regression/test/issue-2659.test.ts
@@ -0,0 +1,33 @@
+import fs from 'node:fs';
+import { builtinModules } from 'node:module';
+import path from 'node:path';
+import { describe, expect, it } from 'vitest';
+
+// https://github.com/zenstackhq/zenstack/issues/2659
+describe('Regression for issue 2659', () => {
+    it('testtools declares every package it imports at runtime', () => {
+        const pkgDir = path.resolve(__dirname, '../../../packages/testtools');
+        const pkg = JSON.parse(fs.readFileSync(path.join(pkgDir, 'package.json'), 'utf-8'));
+        const declared = new Set([...Object.keys(pkg.dependencies ?? {}), ...Object.keys(pkg.peerDependencies ?? {})]);
+
+        const srcDir = path.join(pkgDir, 'src');
+        const imported = new Set<string>();
+        for (const file of fs.readdirSync(srcDir)) {
+            if (!file.endsWith('.ts') || file.endsWith('.d.ts')) {
+                continue;
+            }
+            const content = fs.readFileSync(path.join(srcDir, file), 'utf-8');
+            for (const m of content.matchAll(/^import\s+(?!type\s)[^'"]*?from\s+['"]([^'"]+)['"]/gm)) {
+                const spec = m[1]!;
+                if (spec.startsWith('.') || spec.startsWith('node:') || builtinModules.includes(spec)) {
+                    continue;
+                }
+                const parts = spec.split('/');
+                imported.add(spec.startsWith('@') ? parts.slice(0, 2).join('/') : parts[0]!);
+            }
+        }
+
+        const missing = [...imported].filter((name) => !declared.has(name));
+        expect(missing).toEqual([]);
+    });
+});