helpers.ts

export const pool = (name: string, self: DbTest) => {
  return it(name, async () => {
    return await zdb.serializable(pgpool, async conn => {
      await self(conn);
      await zdb.sql`ROLLBACK`.run(conn);
    });
  });
};

posts.ts

import { it, describe, expect } from './helpers';
import { deletePost, getPosts, createPostTwice } from '~/domain/posts';

describe.concurrent('posts', () => {
  it.pool('returns two values', async conn => {
    const posts = await getPosts(conn);
    expect(posts.length).toEqual(2);
  });

  it.pool('deletes one post', async conn => {
    const posts = await getPosts(conn);
    await deletePost(posts[0].id, conn);
    expect((await getPosts(conn)).length).toEqual(1);
  });
});