Allow globalSetup to pass variables to test suite and globalTeardown

[alesmenzel]

🚀 Feature Proposal

Currently, there is no way (not that I know of) to pass any variable from the globalSetup in order to be able to either use it in the tests or to clear it in the globalTeardown.

Motivation

Imagine the following test case:
I am writing acceptance tests for a logger, that can send the logs to a web server through HTTP. In the test suite, I would like to create a simple HTTP server in the globalSetup and be able to use it in the test suite without the need to specify an own environment (jest-environment-node) that runs for every test file, unlike the globalSetup that runs once.
Then after the tests are done, I would like to be able to close the server in globalTeardown, but currently, there is no way to pass a reference to it.

Example

// globalSetup.js
const createHttpServer = require("./servers/http-server");

module.exports = async () => {
 const http = createHttpServer(5000);
 return { http };
};

// test/spec file
describe("sample-test", () => {
  it("send a request", (next) => {
   const logger = new Logger({ method: "POST", url: "http://localhost:5000" })
   // setup could be exposed as global variable
   global.setup.http.on("request", (req, res) => {
     // ... simplified
     expect(body).toBe("xxx")
     next()
    })
    logger.log("xxx")
  })
})

// globalTeardown.js
module.exports = async (setup) => {
  await promisify(setup.http.close)
};

Pitch

Why does this feature belong in the Jest core platform?

Current global handlers use cases are too limited in order to be useful.

[thymikee]

We won't add this, because globalSetup/Teardown and tests are running in different environments (tests are sandboxed). You'll need to create a custom test environment to inject variables that are e.g. read from the file system: https://jestjs.io/docs/en/configuration#testenvironment-string. See how https://github.com/smooth-code/jest-puppeteer does it

[thymikee]

However, we could discuss the global teardown part, as they run in the same context. What do you think @SimenB?

[SimenB]

Workaround for now is just to assign to a global in setup.

I still think some limited (e.g. json serialized) injection from setup into tests make sense (although that won't cover what OP wants), and we could inject that into teardown as well (not serialized in that case).

[rkuhn]

It should be noted that at least with version 26.4.2 it is possible to compute values in jest.config.js, put them in globalConfig.globals as well as global, and thus have them available both in tests and global setup/teardown functions.

EDIT: This even works when the values are computed asynchronously — just put an object into globalConfig.globals that you also keep a reference to from global and then use globalSetup to fill that object.

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