Jest: Context in before/afterEach calls

[sarenji]

Do you want to request a feature or report a bug?

Bug. Related issues (Jasmine-related): https://github.com/facebook/jest/pull/3506 https://github.com/facebook/jest/issues/3505

What is the current behavior?

The this context is not shared over a single test: Before, during, and after.

If the current behavior is a bug, please provide the steps to reproduce and either a repl.it demo through https://repl.it/languages/jest or a minimal repository on GitHub that we can yarn install and yarn test.

/* eslint-env jest */

beforeEach(function () {
  this.hello = 'hi';
});

afterEach(function () {
  console.log(this.hello);
});

describe('context', () => {
  it('should work', function () {
    console.log(this.hello);
  });
});

What is the expected behavior?

I should see "hi" printed twice. Instead, I see undefined printed twice.

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.

Jest 20.0.1.
Works on 19.0.0.

---

As an aside, I think it's best to recommend against this usage, especially as the style for JavaScript has moved toward () => {} functions rather than function() {} functions. Just dealing with some old code here :) I felt this issue might be helpful in documenting Jasmine's behavior and discussing next steps for Jest.

[thymikee]

_It's not a bug, it's a feature_.
Seriously it is, Jest is not Jasmine and restricts context to test/before/after function scope. Use shared variables outside of test function scope.

let hello;
beforeEach(function () {
  hello = 'hi';
});

afterEach(function () {
  console.log(hello);
});

describe('context', () => {
  it('should work', function () {
    console.log(hello);
  });
});

[artdent]

This was quite the breaking change for us. I wish it had been mentioned in the release notes :-(.

[cpojer]

Apologies, we rewrote Jasmine and this happened as a result of that :(

[skovhus]

jest-codemods can now help people upgrade from older versions of Jest. See https://github.com/skovhus/jest-codemods/releases/tag/0.11.0

FYI @cpojer @thymikee @sarenji

[anatoliyarkhipov]

Just wondering, is there any article with explanation why this was removed?

[mattdell]

It would be great to get an explanation for the removal of this. To me, at least, this seems like a strange convention to enforce.

[Ghirigoro]

As Jest possibly moves towards TypeScript it might be worth revisiting this (or some similar solution for context). If you're using strict types (i.e. no implicit null/undefined) then you're forced to always initialize the local variable when you declare it or else always check that it's initialized:

let aVar:SomeType|undefined = undefined;

// Compiler doesn't know that beforeEach is is going to be called 
// so you have to define the variable above as possibly undefined...
beforeEach( ()=> { aVar = new SomeType; } );

test("A Test", ()=> {
    // Which means you have to ensure that the variable is defined 
    // wherever you use it.
    if (aVar !== undefined) { 
        // do  something with aVar...
    }
});

It's not necessarily a big deal especially if initializing the variable is trivial but if it's complex it can get slightly irritating.

[yss14]

@Ghirigoro

How about

let aVar!: SomeType;

beforeEach( ()=> { aVar = new SomeType; } );

test("A Test", ()=> {
    // do something with aVar without if-statement...
});

This way you have strict null checks for the whole project, but you can mitigate it for test cases on your own risk.

[Ghirigoro]

@yss14

That seems pretty good. I didn't realize you could use the bang operator on declarations. You learn something new every day. Thanks!

[monokrome]

Yo, this needs to be fixed. How is it a "feature"? It's not necessarily a bug, but nobody gets any value out of the scoping not working as expected. It feels like bad design in user experience from the point of view of a user.

[davimello28]

I don't get it. If I run with Jest experimental feature --detectLeak, it clearly says that I should not keep references to the global scope.

Am I losing something important?