jest-mock-extended - call mock with object input [Typescript]

Question

I'm using jest-mock-extended in my tests.

I would like to test the following code:

class A {

  constructor(private b: B){}

  public test(x: string): string {

    const res1 = this.b.compose({
      name: x + '_foo'
    })

    const res2 = this.b.compose({
      name: x + '_bar'
    })
  }

  return res1 + '_' + res2
}

And my test:

test(() => {
  const bMock: MockProxy<B> = mock<B>()
  const a: A = new A(bMock)
  
  bMock.compose.calledWith({
                x: 'yoyo_foo'
            }).mockReturnValueOnce(x + '_once')

  bMock.compose.calledWith({
                x: 'yoyo_bar'
            }).mockReturnValueOnce(x + '_twice')
  //ACT
  const result = a.test('yoyo')

  //ASSERT
  expect(result).toBe('yoyo_foo_once_yoyo_bar_twice)
})

But since the calledWith function is using referential equality it doesn't work, the compose function of the mocked object returns undefined. Is there a way to make it work? Maybe to enforce a shallow equality? I would like to be able to use the calledWith function with an object, is there a way? Is there another way to mock the compose function according to its input?

score 3 · Accepted Answer · answered Jun 09 '21 at 17:58

I think you should use containsValue('value') matcher from jest-mock-extended

in eg.ts file

export interface B {
    compose(obj): string
}

export class A {
    constructor(private b: B) {}

    public test(x: string): string {
        const res1 = this.b.compose({
            name: x + "_foo"
        })

        const res2 = this.b.compose({
            name: x + "_bar"
        })
        return res1 + "_" + res2
    }
}

in eg.test.ts file

// libs
import { test, expect } from "@jest/globals"
import { mock, MockProxy, objectContainsValue } from "jest-mock-extended"

import { A, B } from "./eg"

test("test", () => {
    const bMock: MockProxy<B> = mock<B>()
    const a: A = new A(bMock)

    bMock.compose
        .calledWith(objectContainsValue("yoyo_foo"))
        .mockReturnValueOnce("yoyo_foo" + "_once")

    bMock.compose
        .calledWith(objectContainsValue("yoyo_bar"))
        .mockReturnValueOnce("yoyo_bar" + "_twice")
    //ACT
    const result = a.test("yoyo")

    //ASSERT
    expect(result).toBe("yoyo_foo_once_yoyo_bar_twice")
})

jest-mock-extended - call mock with object input [Typescript]

1 Answers1