Sinon Stub / Spy在单元测试中的本地功能

Question

I use es6 modules and Karma/Mocha/Sinon/Chai for unit testing. If I have an es6 module called within another es6 module I am able to stub/spy on that second es6 module, as seen below:

module-a.js

export function a() {
     // do something
}

module-b.js

import * as moduleA from './module-a';

export function b() {
     // do something
     moduleA.a();
}

With the above code I can spy on moduleA.a() and determine when it was called and stub moduleA.a() and force specific return values.

BUT, if I have this situation instead, I cannot spy or stub:

module-a.js

export function a() {
     // do something
}

export function b() {
     // do something
     a();
}

If I try to spy/stub function a() in this example the spy/stub in Sinon is never called/ This is a pretty common situation so has anyone found a way to spy/stub the local functions?

Thanks!

Answer 1

I had a similar issue and I'm using the following approach where you add a default export that is a named variable wrapper of all of the named function exports. You then prefix your intra-module function calls with that default export object reference. In your test you import the default export and are then able to stub with intra-module function calls respecting the stubbed behavior:

// MyModule.js
let MyModule;

export function myfunc2() { return 2; }
export function myfunc1() { return MyModule.myfunc2(); }

export default MyModule = {
  myfunc1,
  myfunc2
}

// tests.js
import MyModule from './MyModule'

describe('MyModule', () => {
  const sandbox = sinon.sandbox.create();
  beforeEach(() => {
    sandbox.stub(MyModule, 'myfunc2').returns(4);
  });
  afterEach(() => {
    sandbox.restore();
  });
  it('myfunc1 is a proxy for myfunc2', () => {
    expect(MyModule.myfunc1()).to.eql(4);
  });
});