A date created in the test environment and then attached to the global object is not an instance of Date

[nikgraf]

🐛 Bug Report

A date created in the test environment and then attached to the global object is not an instance of Date.

test environment

const NodeEnvironment = require('jest-environment-node')

class MyEnvironment extends NodeEnvironment {
  async setup() {
    await super.setup()
    this.global.someDate = new Date()
  }

test

test("some date to be instance of Date", () => {
  expect(global.someDate instanceof Date).toBe(true); // the result is false
});

To Reproduce

I made an example repository.

Steps to reproduce the behavior:

• attach a Date to global inside a custom test environment
• use instanceof on that variable in the the test

Note: In our case we instantiated a Knex client which we attached to global to instantiate it only once and destroy it only once. Once we ran a query where one entry was a date, but instanceof didn't work.

Expected behavior

global.someDate instanceof Date should be true

Link to repl or repo (highly encouraged)

git clone git@github.com:nikgraf/jest-bug-example.git
yarn
yarn test

Result:

➜  jest-example git:(master) yarn test
yarn run v1.10.1
$ jest
 FAIL  ./index.test.js
  ✓ adding two numbers (2ms)
  ✕ some date to be instance of Date (6ms)

  ● some date to be instance of Date

    expect(received).toBe(expected) // Object.is equality

    Expected: true
    Received: false

       8 |   expect(new Date() instanceof Date).toBe(true);
       9 |   // NOTE this is an object containing methods like getMonth, but isn't a Date instance anymore
    > 10 |   expect(global.someDate instanceof Date).toBe(true);
         |                                           ^
      11 | });

      at Object.toBe (index.test.js:10:43)

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 passed, 2 total
Snapshots:   0 total
Time:        0.328s, estimated 1s
Ran all test suites.
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Run npx envinfo --preset jest

Paste the results here:

npx envinfo --preset jest
npx: installed 1 in 2.133s

  System:
    OS: macOS High Sierra 10.13.6
    CPU: x64 Intel(R) Core(TM) i5-7360U CPU @ 2.30GHz
  Binaries:
    Node: 8.12.0 - ~/.nvm/versions/node/v8.12.0/bin/node
    Yarn: 1.10.1 - /usr/local/bin/yarn
    npm: 6.4.1 - ~/.nvm/versions/node/v8.12.0/bin/npm
  npmPackages:
    jest: ^23.6.0 => 23.6.0 

[SimenB]

This is expected - the global Date inside and outside of the sandbox is not the same.

You can work around it by doing this.global.someDate = new this.global.Date().

If you want to create something in the custom environment using the same globals, you need to execute it inside of the vm this.executeScript.

Also sorta dupe of #2549, although your use case (creating something outside of the sandbox and using it inside of it) is not really supported - it breaks the abstraction.

You might consider using setupFiles instead

[nikgraf]

@SimenB thanks for the clarification

From what I understood setupFiles won't work, because knex keeps a DB connection open and then the test execution never finishes.

Regarding your workaround. In which file would I place this.global.someDate = new this.global.Date()?

Also I'm not fully understanding this.executeScript. I was looking up the Node docs for vm, but there is no executeScript afaik.

[github-actions]

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