jest: Jest 27: incorrect `afterEach` order with `jest-circus`

Hi @jeysal ,

I would still vote for fixing a bug instead of documenting it.

There are many testing libraries around, which use hooks under the hood, and the expectation is that the order of their execution will be respected, as it is in all other testing frameworks. Not sure why jest decided to invent own way and to cause issues.

Let’s take a look at a simple example: we want to backup a global variable for a test, and restore it afterwards. To avoid copy-pasting of tons of lines of code, we decided to write a helper function:

const backupTest = (newValue: typeof globalVar): void => {
  let backup: typeof globalVar;

  beforeEach(() => {
    backup = globalVar;
    globalVar = newValue;
  });

  afterEach(() => {
    globalVar = backup;
  });
};

The idea is simple, our test should look like that:

describe('globalVar', () => {
  backupTest(1);

  it('equals 1', () => {
    expect(globalVar).toEqual(1);
  });
});

so instead of having 10 lines of code how to backup globalVar for each test, we have just 1.

Now, let’s imagine that globalVar isn’t primitive, but a complex object and backupTest does only 1 modification, whereas we need an additional modification, for example, another group of stub members.

In all testing libraries it will look like that:

describe('globalVar', () => {
  backupTest(1); // one group of stub members.
  backupTest(2); // another group of stub members.

  // tests
});

and it works well, after the test, globalVar will have its initial value before the suite, because the first executed afterEach belongs to 2 and the second executed afterEach belongs to 1.

However, with the new changes in jest, globalVar is going to be 1, because of the broken order, because first jest executes afterEach for 1, and then afterEach for 2, which restores a wrong value.

let globalVar = 0;

const backupTest = (newValue: typeof globalVar): void => {
  let backup: typeof globalVar;

  beforeEach(() => {
    backup = globalVar;
    globalVar = newValue;
  });

  afterEach(() => {
    globalVar = backup;
  });
};

describe('backup', () => {
  it('equals 0 before all', () => {
    expect(globalVar).toEqual(0);
  });

  describe('globalVar', () => {
    backupTest(1); // setting globalVar to 1 and restoring it to 0 afterwards
    backupTest(2); // setting globalVar to 2 and restoring it to 1 afterwards

    it('equals 2 before each', () => {
      expect(globalVar).toEqual(2);
    });

    describe('each', () => {
      backupTest(3); // setting globalVar to 3 and restoring it to 2 afterwards
      backupTest(4); // setting globalVar to 4 and restoring it to 3 afterwards

      it('equals 4 after each', () => {
        expect(globalVar).toEqual(4);
      });
    });

    it('resets to 2 after each', () => {
      expect(globalVar).toEqual(2);
    });
  });

  it('resets to 0 after all', () => {
    expect(globalVar).toEqual(0);
  });
});

which fails on jest as

    expect(received).toEqual(expected) // deep equality

    Expected: 0
    Received: 1

      42 |
      43 |   it('resets to 0 after all', () => {
    > 44 |     expect(globalVar).toEqual(0);
         |                       ^
      45 |   });
      46 | });
      47 |

proposed fix long time ago: https://github.com/jestjs/jest/pull/12861

This is still relevant. 😎

Still experiencing this issue with jest-circus… For now we have unblocked ourselves from upgrading past Jest 26 by using explicitly specifying jest-jasmine2 as our test runner.

do not close, please

In that specific case, you can probably do

afterEach(() => {
  try {
    expect(nock).toBeDone();
  } finally {
    nock.cleanAll();
  }
});