Sinon.stub.resolves returns undefined when awaited within Buffer.from

Question

I have the following code:

 describe('run()', () => {
    const ret = ['returnValue'];
    const expectedData = 'data';

    beforeEach(() => {
      sinon.stub(myStubbedService, 'myStubbedMethod').resolves(ret);
    });
    it('should not break', async () => {
      const foo = myStubbedService.myStubbedMethod();
      const bar = await myStubbedService.myStubbedMethod();
      const works = Buffer.from(bar[0], 'hex');
      console.log(works);
      const breaks = Buffer.from(await myStubbedService.myStubbedMethod()[0], 'hex');

      console.log(breaks);
    })

logging works logs the correct Buffer but logging breaks =>

TypeError [ERR_INVALID_ARG_TYPE]: The first argument must be of type string or an instance of Buffer, ArrayBuffer, or Array or an Array-like Object. Received undefined

I am pretty sure the code for breaks works just the same as the code for works but the test fails. What am I missing?

Answer 1

Actually, your way to get the works is not the same as breaks. The way to get the works is easy to understand - Wait for the response of myStubbedMethod, then get the first item of the response.

Take a look at the way you get the breaks:

const breaks = Buffer.from(await myStubbedService.myStubbedMethod()[0], 'hex');

(Maybe) as you know myStubbedService.myStubbedMethod() return a Promise, when you get the 0 attribute of a Promise, you get back an undefined value. await with a constant, you get the constant.

Your code will look like this:

const breaks = Buffer.from(await undefined, 'hex');

Just more parentheses:

const breaks = Buffer.from((await myStubbedService.myStubbedMethod())[0], 'hex');