diff --git a/src/tests/setup/mock-db.ts b/src/tests/setup/mock-db.ts
index 0f8b6b09..f5183fe6 100644
--- a/src/tests/setup/mock-db.ts
+++ b/src/tests/setup/mock-db.ts
@@ -1,29 +1,25 @@
 import { vi } from 'vitest';
-import pg from 'pg';
 import dotenv from 'dotenv';
 
 // Load test-specific environment variables
 dotenv.config({ path: '.env.test' });
 
-const { Pool } = pg;
-
 vi.mock('pg', async (importOriginal) => {
   const pg = await importOriginal<typeof import('pg')>();
 
-  // Create the singleton test pool instance *before* mocking the Pool constructor.
-  // This instance will be shared across all tests that import the db services.
-  const testPool = new pg.Pool({
-    connectionString: process.env.DATABASE_URL,
-  });
+  // This is the mock pool instance that will be returned by the Pool constructor.
+  // It mocks the methods that our application's db service uses.
+  const mPool = {
+    connect: vi.fn(),
+    query: vi.fn(),
+    on: vi.fn(),
+    end: vi.fn(),
+  };
 
   return {
     ...pg,
-    // Override the Pool constructor. Now, any module that calls `new Pool()`
-    // will receive our singleton `testPool` instance.
-    // We use `mockImplementation` to return the instance, which is the correct
-    // way to mock a class constructor that should return a specific instance.
-    Pool: vi.fn().mockImplementation(() => {
-      return testPool;
-    }),
+    // The original mock was an arrow function, which cannot be called with `new`.
+    // Using vi.fn() creates a mock constructor that returns our mock pool instance.
+    Pool: vi.fn(() => mPool),
   };
 });
\ No newline at end of file
diff --git a/vite.config.ts b/vite.config.ts
index 7f65a318..fc722bc0 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -29,8 +29,13 @@ export default defineConfig({
     environment: 'jsdom',
     globalSetup: './src/tests/setup/global-setup.ts',
     setupFiles: ['./src/vitest.setup.ts'],
-    // Exclude integration tests, which are handled by a separate project.
-    exclude: ['**/*.integration.test.ts', '**/node_modules/**'],
+    // Exclude integration tests and other non-test files from the unit test runner.
+    exclude: [
+      '**/node_modules/**',
+      '**/dist/**',
+      '**/*.integration.test.ts',
+      '**/*.e2e.test.ts'
+    ],
     coverage: {
       provider: 'v8',
       reporter: ['text', 'html'],
diff --git a/vitest.config.integration.ts b/vitest.config.integration.ts
index 2e72af0f..1f515551 100644
--- a/vitest.config.integration.ts
+++ b/vitest.config.integration.ts
@@ -13,7 +13,7 @@ export default defineConfig({
     // This setup script starts the backend server before tests run.
     globalSetup: './src/tests/setup/integration-global-setup.ts',
     testTimeout: 15000, // Increased timeout for server startup and API calls.
-    // "singleThread: true" is deprecated in modern Vitest.
+    // "singleThread: true" is removed in modern Vitest.
     // Use fileParallelism: false to ensure test files run one by one to prevent port conflicts.
     fileParallelism: false,
   },