Nest.js Test Setup with In Memory Postgres Database (pg-mem)

setup.ts

// Install npm i pg-mem --save-dev

import { DataSource, Repository } from 'typeorm';
import { newDb, DataType } from 'pg-mem';
import { v4 } from 'uuid';

const setupDataSource = async () => {
  const db = newDb({
    autoCreateForeignKeyIndices: true,
  });

  db.public.registerFunction({
    implementation: () => 'test',
    name: 'current_database',
  });

  db.registerExtension('uuid-ossp', (schema) => {
    schema.registerFunction({
      name: 'uuid_generate_v4',
      returns: DataType.uuid,
      implementation: v4,
      impure: true,
    });
  });

  const ds: DataSource = await db.adapters.createTypeormDataSource({
    type: 'postgres',
    entities: [__dirname + '/../../src/**/*.entity{.ts,.js}'],
  });
  await ds.initialize();
  await ds.synchronize();
  
  return ds;
};

test-module.ts

export const buildTestingModule = async () => {
  if (testingModule) {
    return testingModule;
  }

  const dataSource = await setupDataSource();
  testingModule = await Test.createTestingModule({
    imports: [
      TypeOrmModule.forRoot({
        name: 'default',
        synchronize: true,
      }),
      CoreModule,
    ],
  })
    .overrideProvider(DataSource)
    .useValue(dataSource)
    .compile();

  return testingModule;
};