flyer-crawler.projectium.com/src/tests/setup/mock-db.ts

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,
  });

  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;
    }),
  };
});