node.js - Why am I getting "Error: Resolution method is overspecified"?

Question

After the upgrade, Mocha can not even run a simple test here is the code

const assert = require('assert');

it('should complete this test', function (done) {
  return new Promise(function (resolve) {
    assert.ok(true);
    resolve();
   })
  .then(done);
});

I took this code from here

I understood that it now throws an exception Error: Resolution method is overspecified. Specify a callback * or * return a Promise; not both.

But how to make it work? I did not understand. I have

node -v 6.9.4

mocha -v 3.2.0

How to run this code are now in a new and correct format?

Answer 1

Just drop
.then(done); and replace function(done) with function()

You are returning a Promise so calling done is redundant as it said in error message

In the elder versions you had to use callback in case of async methods like that

it ('returns async', function(done) {
   callAsync()
   .then(function(result) {
      assert.ok(result);
      done();
   });
})

Now you have an alternative of returning a Promise

it ('returns async', function() {
  return new Promise(function (resolve) {
     callAsync()
       .then(function(result) {
          assert.ok(result);
          resolve();
       });
  });
})

But using both is misleading (see for example here https://github.com/mochajs/mocha/issues/2407)