如何使用testEnvironment作为NodeEnvironment启动快速服务器？

Question

调查了问题Async setup of environment with Jest之后，我能够做到这一点：

package.json

{
  "name": "my-project",
  "jest": {
    "testEnvironment": "./test_environment.js",
  }
}

test_environment.js

const express = require('express');
const NodeEnvironment = require('jest-environment-node');

class ExpressEnvironment extends NodeEnvironment {
  constructor(config, context) {
    super(config, context);
  }

  async setup() {
    await super.setup();
    const app = express();

    this.global.server = app.listen(0, "127.0.0.1", () => {
        console.log(`Running express server on '${JSON.stringify(server.address())}'...`);

        how to make setup() wait until app.listen callback is finished, 
        i.e., the server has properly started.

    });
    app.use(express.static('../testfiles'));
  }

  async teardown() {
    this.global.server.close();
    await super.teardown();
  }

  runScript(script) {
    return super.runScript(script);
  }
}

module.exports = ExpressEnvironment;

如何使setup()等待app.listen()回调完成，即服务器已正确启动？

[之前，当我使用beforeAll()时，我的代码运行良好，因为我可以使用done()传递的beforeAll()异步回调：

const express = require('express');
const app = express();
var server;

beforeAll(async (done) => {
    server = app.listen(0, "127.0.0.1", () => {
        console.log(`Running express server on '${JSON.stringify(server.address())}'...`);
        done();
    });
    app.use(express.static('../testfiles'));
});

afterAll(() => {
    server.close();
});

与NodeEnvironment done()函数上的beforeAll setup()回调等效吗？

Answer 1

您可以通过甚至等待侦听，将其包装在promise中，然后将promise解析为服务器侦听的回调来执行此操作

  const app = express();
  let server;
  await new Promise(resolve => server = app.listen(0, "127.0.0.1", resolve));
  this.global.server = server;

您还可以放置一个自定义的回调，该回调仅将promise解析器作为app.listen()的第三个参数，它应运行该代码，然后在需要某种诊断时调用resolve。

Answer 2

扩展Robert Mennell答案：

您还可以放置一个自定义的回调，该回调仅将promise解析器作为app.listen()的第三个参数，它应运行该代码，然后在需要某种诊断时调用resolve。

let server;
const app = express();

await new Promise(function(resolve) {
    server = app.listen(0, "127.0.0.1", function() {
        console.log(`Running express server on '${JSON.stringify(server.address())}'...`);
        resolve();
    });
});
this.global.server = server;