[jest-plugin-set] Set variables should be created before beforeEach is called

[negativetwelve]

Description

Nested set calls must ALL come before beforeEach in order to be set properly. Otherwise, it'll use the values from outer set calls which is incorrect

Screenshot

Test Plan

[bxt]

@negativetwelve I wonder what this is about. When you mix in own beforeEach blocks and use values previously defined with set in them? Because this seems to work just fine:

import set from 'jest-plugin-set';

set('foo', () => 'outer');
set('bar', () => `bar with foo: ${foo}`);
set('baz', () => `baz with bam: ${bam}`);

describe('outer', () => {
  set('foo', () => 'inner');
  set('bam', () => 'yey');
  it('uses the inner foo for calculating bar', () => {
    expect(bar).toEqual('bar with foo: inner');
  });
  it('uses the inner bam for calculating baz', () => {
    expect(baz).toEqual('baz with bam: yey');
  });
});

[negativetwelve]

Hi @bxt, thanks for your comment. If I remember correctly, the issue comes from something like:

import set from 'jest-plugin-set';

describe('outer', () => {
  set('a', () => 1);
  set('b', () => a);

  beforeEach(() => {
    console.log(a, b);
  });

  describe('inner', () => {
    set('a', () => 5);

    beforeEach(() => {
      console.log(a, b);
    });

    it('returns the correct value', () => {
      expect(a + b).toEqual(10);
    });
  });
});

It will log:

1, 1
1, 1

when it should be:

1, 1
5, 5

and if I remember correctly, the test should fail on this and return 2 instead of 10. Let me know if you're seeing the same behavior.

(I wrote the code without testing, please excuse if there are small errors)

[bxt]

Hey @negativetwelve, wow thank you for your fast answer! It also fails for me but slightly different. It outputs

1 1
5 1

And:

    Expected value to equal:
      10
    Received:
      6

So only the indirect calculation of b has the problem. Interestingly the beforeEach also messes with the assertion, because the bad value will be cached then.

(node v10.7.0, [email protected], [email protected])

I think one can get rid of all beforeEach uses with set though 😅

[negativetwelve]

oops you're right (I kept editing my responses haha). It's definitely a caching issue because of the order that the beforeEach are run in.

I stumbled upon this issue when using set to construct something like a user object and changing one value within a nested set of describe blocks. It wasn't too hard to work around but was definitely unexpected.

I mainly use set for variable assignment and beforeEach for actions and things like requests.

beforeEach(() => {
  fetch(url, params);
});

something like this ^

[timscott]

I ran into this also today. Here's another repro.

describe('', () => {
  set('a', () => x)
  beforeEach(() => {
    console.log(a);
  })
  describe('', () => {
    set('x', () => 1)
    test('', () => {
      expect(a).toEqual(1)
    })
  })
})

Fails with ReferenceError: x is not defined on the second line.

Pulling variables from inner contexts to use in beforeEach is definitely a useful pattern which can eliminate a lot of duplicate code. Something I always do in rspec.