mock + toBeCalledWith function and modified objects

[mikamikuh]

🐛 Bug Report

expect(mock).toBeCalledWith(...) function doesn't compare objects with the state when it was called. It seems to be holding the reference to the object, so when the mock function was called with an object reference to { a: 'foo' } and the object was updated afterwards, expect(mock).toBeCalledWith(...) compares with the latest state of the object, not { a: 'foo' }.

To Reproduce

Steps to reproduce the behavior:

Implementation with update obj after the fn function was called, so it should be called with { a: 'foo' }

const objectUpdate = (fn) => {
  const obj = {
    a: 'foo'
  }
  fn(obj)
  obj.b = 'bar'
}

and, in the test, pass jest.fn() to the fucntion (objectUpdate)

test ('Test with object update', () => {
  const mock = jest.fn()
  objectUpdate(mock)
  expect(mock).toBeCalledWith({
    a: 'foo'
  })
})

which fails with:

    - Expected
    + Received

      Object {
        "a": "foo",
    +   "b": "bar",
      },

Expected behavior

The test above should pass because when the fn function is called, the obj is just { a: 'foo' }.

Link to repl or repo (highly encouraged)

https://replit.com/@mikamikuh/jest-playground#object-update.js

envinfo

  System:
    OS: Linux 5.8 Ubuntu 20.04.2 LTS (Focal Fossa)
    CPU: (12) x64 AMD Ryzen 5 3600 6-Core Processor
  Binaries:
    Node: 12.13.0 - ~/.nvm/versions/node/v12.13.0/bin/node
    npm: 6.12.0 - ~/.nvm/versions/node/v12.13.0/bin/npm

[SimenB]

Duplicate of #10373 (and that itself is a duplicate of an older issue I'm currently unable to find...)

[github-actions]

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