Jest spyOn函数不是Class或Object类型

Question

I am familiar with setting spies on Class or Object methods, but what about when the function is just an export default - such that the method itself is independent, like a utility?

I have some existing code like so:

const Funct1 = props => {
  if(props){
    Funct2(args);
  }
  // or return something
};
const Funct2 = props => {
  // do something
  return true
};
export default Funct1;  //Yes the existing export is named the same as the "entry" method above.

And, for example, I'd like to spy on Funct1 getting called and Funct2 returns true.

import Funct1 from "../../../src/components/Funct1";
describe("Test the Thing", () => {
    it("New Test", () => {
        let props = {
            active: true,
            agentStatus: "online"
        };
        const spy = spyOn(Funct2, "method name"); <-- how doe this work if not an obj or class?

        Funct1(props);
        //If I try Funct2(props) instead, terminal output is "Funct2 is not defined"

        expect(spy).toHaveBeenCalledWith(props);
    });
});

Answer 1

I am not expert in jest, but my recommendation to think about:

1) When the function is exported as default I use something like:

import Funct1 from "../../../src/components/Funct1";
...
jest.mock("../../../src/components/Funct1");
...
expect(Funct1).toHaveBeenCalledWith(params);

2) When the module (utils.js) has multiple exports as

export const f1 = () => {};
...
export const f8 = () => {};

You can try

import * as Utils from "../../../src/components/utils"
const f8Spy = jest.spyOn(Utils, 'f8');
...
expect(f8Spy).toHaveBeenCalledWith(params);

Similar discussion here

Answer 2

I believe that is not possible to test Funct1 calling Funct2 without modifying the existing code. If the latter is an option, here are two options to introduce dependency injection:

• Create and export a factory function:

   const Funct2 = props => { // do something return true; }; const Funct1 = CreateFunct1(Funct2); export function CreateFunct1(Funct2) { return props => { if (props) { Funct2(props); } // or return something }; } export default Funct1; // and here is the test: describe('Test the Thing', () => { it('New Test', () => { // Arrange const funct2Spy = jasmine.createSpy('Funct2'); const funct1 = CreateFunct1(funct2Spy); const props = "some data"; // Act funct1(props); // Assert expect(funct2Spy).toHaveBeenCalledWith(props); }); }); 

• Export Funct2 too. Here is a thread on this topic. Maybe its example would have to be tweaked a little bit for your scenario because of the export syntax.