How to mock/replace getter function of object with Jest?

问题

In Sinon I can do the following:

var myObj = {
    prop: 'foo'
};

sinon.stub(myObj, 'prop').get(function getterFn() {
    return 'bar';
});

myObj.prop; // 'bar'

But how can I do the same with Jest? I can't just overwrite the function with something like jest.fn(), because it won't replace the getter

"can't set the value of get"

回答1:

You could use Object.defineProperty

Object.defineProperty(myObj, 'prop', {
  get: jest.fn(() => 'bar'),
  set: jest.fn()
});

回答2:

For anyone else stumbling across this answer, Jest 22.1.0 introduced the ability to spy on getter and setter methods.

Edit: like in scieslak's answer below, because you can spy on getter and setter methods, you can use Jest mocks with them, just like with any other function:

class MyClass {
  get something() {
    return 'foo'
  }
}

jest.spyOn(MyClass, 'something', 'get').mockReturnValue('bar')
const something = new MyClass().something

expect(something).toEqual('bar')

回答3:

OMG I've been here so many times. Finally figure out the proper solution for this. If you care about spying only. Go for @Franey 's answer. However if you actually need to stub a value for the getter this is how you can do it

class Awesomeness {
  get isAwesome() {
    return true
  }
}

describe('Awesomeness', () => {
  it('is not always awesome', () => {
    const awesomeness = new Awesomeness
    jest.spyOn(awesomeness, 'isAwesome', 'get').mockReturnValue(false)

    expect(awesomeness.isAwesome).toEqual(false)
  })
})

来源：https://stackoverflow.com/questions/43697455/how-to-mock-replace-getter-function-of-object-with-jest

标签

javascript

reactjs

mocking

sinon

jestjs