Database/network tests are isolated from production data

Tests that write to a database without a separate test database URL will insert, update, and delete rows in the development database. Over time this pollutes developer workflows with synthetic data, breaks count-based assertions as rows accumulate, and creates the risk that a destructive test (deleteMany, truncate) runs against real data if configuration is accidentally shared across environments. ISO-25010:2011 recoverability requires that test execution be isolated from other system states.

Create a .env.test file with a separate DATABASE_URL pointing to a dedicated test database. Reference it explicitly in vitest.config.ts or your test runner configuration so it's impossible to accidentally run tests against the dev database:

# .env.test
DATABASE_URL=postgresql://user:pass@localhost:5432/myapp_test

// vitest.config.ts
export default defineConfig({
  test: {
    env: { DATABASE_URL: process.env.TEST_DATABASE_URL ?? '' },
    setupFiles: ['./tests/setup.ts'],
  },
})