How to properly stub a function return value?

Question

• Premise: JS ES6, NodeJS
• Testing Framework: TAP
• Mocking Library: testdouble.js

---

I am attempting to mock the return value for the method of my class and keep receiving this error:

not ok Unsatisfied verification on test double. Wanted: - called with (true). But there were no invocations of the test double.

Here is my testing code:

// Imports for unit testing
const tap = require('tap');
const Subject = require('../src/iTunesClient.js');
const td = require('testdouble');

let reqJson;

// Ensure the iTunes class methods are called
tap.test('iTunesClient class methods function as intended', (t) => {
  t.beforeEach((ready) => {
    reqJson = td.replace('../src/reqJson.js');
    ready();
  });

  t.afterEach((ready) => {
    td.reset();
    ready();
  });

  t.test('iTunesClient.getData', (assert) => {
    const callback = td.function();
    const subject = new Subject();
    subject.setTerm('abc 123');
    subject.setURL();

    td.when(reqJson.get(td.callback)).thenCallback(true);

    subject.getData(callback);

    td.verify(callback(true));
    assert.end();
  });

  t.end();
});

Specifically, this line is related to my issue:

td.verify(callback(true));

How can I fake the callback value of true for reqJson.get()? Right now, Subject.geData() is a method of the iTunesClient class which calls another file, reqJson.js, to use its exported get() method.

Answer 1

I wanted to update this question, as I recently solved this issue. Essentially, I had two issues:

1. Account for both reqJson function parameters
2. Account for all callback return values

Per testdouble documentation for item 1:

When passed td.matchers.anything(), any invocation of that test double function will ignore that parameter when determining whether an invocation satisfies the stubbing.

Hence, I adjusted my line of code as follows:

Before: td.when(reqJson.get(td.callback)).thenCallback(true);

After: td.when(reqJson.get(td.matchers.anything(), td.callback)).thenCallback(null, null, null);