How to find a specific object key in jest

We’ve all been there, writing a jest test and having that one case where we want to have a very specific key in an object.

our first attempt might be

it("should redirect to correct url if id is incorrect", () => {
  const mockFn = jest.fn()

  mockRouter.query = {
    id: "id2",
  }
  mockRouter.push = mockFn

  render(<Component>I am visible</Component>)

  expect(mockFn).toHaveBeenCalledWith({
    query: { id: "id1" },
  })
})

This will throw us an error like this

Error: expect(jest.fn()) .toHaveBeenCalledWith(...expected)

Solution

Since Jest 18 we are able to use objectContaining . This makes it super easy to check for 1 or more specific keys:

it("should redirect to correct url if id is incorrect", () => {
  const mockFn = jest.fn()

  mockRouter.query = {
    id: "id2",
  }
  mockRouter.push = mockFn

  render(<Component>I am visible</Component>)

  expect(mockFn).toHaveBeenCalledWith(
    expect.objectContaining({
      query: { id: "id1" },
    })
  )
})

this test will pass.

Alternative solutions

in the case that you only have a few keys you could also use expect.anything()

this would be used like so:

expect(mockFn).toHaveBeenCalledWith({
   query: { id: "id1" },
   key: expect.anything(),
   key2: expect.anything()
})

Conclusion

there are 2 options to find a specific key in objects. objectContaining and expect.anything()