Jest beforeAll() share between multiple test files - jestjs

Question

I have a Node.js project that I'm testing using Jest. I have several test files that have the same setup requirement. Previously, all these tests were in one file, so I just had a beforeAll(...) that performed the common setup. Now, with the tests split into multiple files, it seems like I have to copy/paste that beforeAll(...) code into each of the files. That seems inelegant - is there a better way to do this, ideally where I can just write my beforeAll(...)/setup logic once, and "require" it from multiple test files? Note that there are other tests in my test suite that don't require this setup functionality, so I don't want to make all my tests run this setup (just a particular subset of test files).

Answer 1

If you're using Jest >=20, you might want to look into creating a custom jest-environment for the tests that require this common setup. This would be a module that extends either jest-environment-node or jest-environment-jsdom, and implements async setup(), async teardown(), and async runScript() to do this setup work.
You can then add a #jest-environment my-custom-env directive to those files that require this setup.
See the Jest config docs for testEnvironment for details on how to set this up; there's a simple example there.

Answer 2

I am using a simple "test hooks" pattern for this:
// This function wraps beforeAll and afterAll into a single RAII-like call.
// That makes the describe code further down easier to read and makes
// sure you don't forget the afterAll part. Can easily be shared between tests.
function useFakeServer() {
let server;
beforeAll(() => server = sinon.fakeServer.create());
afterAll(() => server.restore());
return () => server;
}
describe('Some scenario', () => {
const getServer = useFakeServer();
it('accesses the server', () => {
const server = getServer();
// Test as you normally would..
expect(server.requests[0]. /* ... */);
});
});

Answer 3

If you need a script to run before all your test files, you can use globalSetup
This option allows the use of a custom global setup module which exports an async function that is triggered once before all test suites.
in your jest.config.js
//jest.config.js
module.exports = {
...
testTimeout: 20000,
globalSetup: "./setup.js"
};
then create a file named setup.js
// setup.js
module.exports = async () => {
console.log("I'll be called first before any test cases run");
//add in what you need to do here
};
Docs

Answer 4

You can move your beforeAll logic into one file and reference it in jest.config.js setupFilesAfterEnv section:
module.exports = {
...
setupFilesAfterEnv: ['<rootDir>/testHelper.ts'],
...
}
https://jestjs.io/docs/en/configuration#setupfilesafterenv-array

Answer 5

Create a function somewhere like so:
export function setupBeforeAndAfter(putParamsHereIfYouHaveAny) {
beforeAll(() => shared-before-all-code);
afterAll(() => shared-after-all-code);
beforeEach(() => shared-before-each-code);
afterEach(() => shared-after-each-code);
}
Then just call it wherever you would otherwise have manually written these functions:
describe('My test', () => {
setupBeforeAndAfter(putParamsHereIfYouHaveAny)
it('is amazing', () => {
// Stuff in setupBeforeAndAfter() will run before/after this test as appropriate
})
})