NestJs Testing create a single instance of app across all tests - nestjs

Question

I am running into the issue Error querying the database: db error: FATAL: sorry, too many clients already and I am convinced it is because a new instance of the app is being instantiated for every test suite. I have attempted to break the app creation out into a helper file, and that file looks as follows
import { INestApplication } from '#nestjs/common';
import { Test, TestingModule } from '#nestjs/testing';
import { AppModule } from '../../src/app.module';
import { PrismaService } from '../../src/prisma.service';
declare global {
var app: INestApplication | undefined;
}
export const getApp = async () => {
if (global.app) {
return global.app;
}
const moduleFixture: TestingModule = await Test.createTestingModule({
imports: [AppModule],
providers: [PrismaService],
}).compile();
const app = moduleFixture.createNestApplication();
await app.init();
global.app = app;
return app;
};
This however does not work, when I add console logs, I can see that app is being instantiated for every test suite.
This is how my typical before hook looks
beforeAll(async () => {
const moduleFixture: TestingModule = await Test.createTestingModule({
imports: [AppModule],
}).compile();
app = moduleFixture.createNestApplication();
await app.init();
});

Answer 1

I had the same issue and solved it by using Jest's globalSetup and globalTeardown options. I create one instance of the app and seed the DB before running the tests, and destroy it and run the teardown when they've finished. I use a global variable to reference the app instance.
In my jest-e2e.json:
{
...
"globalSetup": "<rootDir>/test/test-setup.ts",
"globalTeardown": "<rootDir>/test/test-teardown.ts"
}
test-setup.ts:
import * as fs from 'fs';
import { FastifyAdapter, NestFastifyApplication } from '#nestjs/platform-fastify';
import { Test } from '#nestjs/testing';
import { AppModule } from './../src/app.module';
import { WriteDataSource } from './../src/database/database.module';
module.exports = async () => {
const moduleRef = await Test.createTestingModule({
imports: [ AppModule ]
})
.compile();
global.app = moduleRef.createNestApplication<NestFastifyApplication>(
new FastifyAdapter()
);
await global.app.init();
await global.app.getHttpAdapter().getInstance().ready();
const seedQuery = fs.readFileSync(__dirname + '/scripts/database-seed.sql', { encoding: 'utf-8' });
await WriteDataSource.manager.query(seedQuery);
};
test-teardown.ts:
import * as fs from 'fs';
import { WriteDataSource } from '../src/database/database.module';
module.exports = async () => {
const teardownQuery = fs.readFileSync(__dirname + '/scripts/database-teardown.sql', { encoding: 'utf-8' }).replace(/\n/g, '');
await WriteDataSource.query(teardownQuery);
await WriteDataSource.destroy();
await global.app.close();
};

Answer 2

I solved it by exporting the server instance and everything else i needed:
let server: Server
let app: INestApplication
let testService: TestService
export const initServer = async () => {
const module = Test.createTestingModule({
imports: [AppModule, TestModule]
})
const testModule = await module.compile()
app = testModule.createNestApplication()
app.useGlobalPipes(
new ValidationPipe({
whitelist: true
})
)
server = app.getHttpServer()
testService = app.get(TestService)
await app.init()
}
export { app, server, testService }
Here i exported the function to clear all my databases to use where needed:
export const clearAllDatabases = async () => {
models.map(async (model: any) => {
await model.destroy({
where: {},
truncate: true,
cascade: true
})
})
}
import { app, initServer } from '#tests/resources/config/test-server'
import { clearAllDatabases } from '#tests/resources/config/clear-databases'
export const setupTestData = async () => {
await initServer()
await clearAllDatabases()
await userRegister()
await app.close()
}