toBeShallowInstanceOf

toBeShallowInstanceOf.spec.js

expect.extend({
  toBeShallowInstanceOf(received, argument) {
    const pass = Object.getPrototypeOf(received) === argument.prototype
    return {
      message: () => (pass ? 'OK' : 'KO'),
      pass,
    }
  },
})

function Car(make, model, year) {
  this.make = make
  this.model = model
  this.year = year
}

const mycar = new Car('Honda', 'Accord', 1998)

test('toBeShallowInstanceOf', () => {
  expect(mycar).toBeShallowInstanceOf(Car)
  expect(mycar).toBeInstanceOf(Car)

  expect(mycar).not.toBeShallowInstanceOf(Object)
  expect(mycar).toBeInstanceOf(Object)
})