单元测试链式承诺

Question

How would I unit test a class method that calls an imported class's method that is a promise? I have the following structure:

import { SomeClass } from 'some-library';

class MyClass extends AnotherClass {
  myMethod() {
    const someClass = new SomeClass();

    return someClass.somePromiseMethod('someParam')
      .then(response => response.data)
      .then(response => {
        // Do stuff
      });
  }
}

I have the following test

describe('myMethod', () => {
  it('does something', async () => {
    const inst = new MyClass();
    const stub = sinon.stub(SomeClass, 'somePromiseMethod')
      .resolves(Promise.resolve({
        data: [],
      }));

    await inst.myMethod();

    expect(stub.callCount).to.equal(1);
  });
});

Which is still pretty bare as I'm not sure how to approach this. Would it be better to break down the code in the then s?

UPDATE

Apparently SomeClass is a singleton and sinon was throwing an error saying somePromiseMethod is a non-existent own property . I changed the stub to call on its prototype instead and now the stub is being called.

class MyClass extends AnotherClass {
  myMethod() {
    const someClassInstance = SomeClass.getInstance();

    return someClassInstance.somePromiseMethod('someParam')
      .then(response => response.data)
      .then(response => {
        // Do stuff
      });
  }
}


describe('myMethod', () => {
  it('does something', async () => {
    const inst = new MyClass();
    const stub = sinon.stub(SomeClass.prototype, 'somePromiseMethod')
      .resolves(Promise.resolve({
        data: [],
      }));

    await inst.myMethod();

    expect(stub.callCount).to.equal(1);
  });
});

Now, since then second then would just return data , I could just put //Do stuff in a separate function and test that.

Answer 1

You are stubbing out the wrong method somePromiseMethod exists on the prototype of SomeClass so you need to stub that instead. Sinon should let you do something like:

const stub = sinon.stub(SomeClass.prototype, 'somePromiseMethod')
  // You may be able to remove the Promise.resolve as well, as I think resolves does this for you
  .resolves({
    data: [],
  });