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Javascript promise never resolves

I am using rotateByDegrees from a library called node-poweredup in a typescript project:
motor.rotateByDegrees(20,10).then(function(value) {console.log("test");}, function(value) {console.log("error");});
I would expect to see "test" after successful completion, but the promise never resolves. If I use await, it hangs on the await line forever.
Replicating the syntax that appears to be used in the rotateByDegrees function:
let promise = new Promise((resolve) => { return resolve(); });
does not compile, I get error TS2794: Expected 1 arguments, but got 0. Did you forget to include 'void' in your type argument to 'Promise'? I can make it compile and behave as expected with resolve(true), but how does it compile in the library then? Do I misunderstand promises? Some feature in typescript? A bug in the library? I am a newbie to JavaScript, I don't want to over-complicate this question by including irrelevant details. If you can give me hints on what I am missing and how to debug this, I can provide all relevant details.

Thanks to the helpful comments I was able to narrow it down to the compilation of the library. I did in fact not use a pre-compiled binary but had to compile the library myself using electron-rebuild to make the bluetooth adapter work. I did the following test:
git clone https://github.com/nathankellenicki/node-poweredup.git
cd node-poweredup
npm install
npm run build
this compiles without error. I created the following test file
const PoweredUP = require("node-poweredup");
const poweredUP = new PoweredUP.PoweredUP();
poweredUP.scan(); // Start scanning for hubs
console.log("Looking for Hubs...");
poweredUP.on("discover", async (hub) => { // Wait to discover hubs
await hub.connect(); // Connect to hub
console.log(`Connected to ${hub.name}!`);
const motorA = await hub.waitForDeviceAtPort("A"); // Make sure a motor is plugged into port A
motorA.rotateByDegrees(20,10).then(function(value) {console.log("test");});
});
and get the expected output:
node-poweredup$ node test.js
Looking for Hubs...
Connected to MyHub2!
test
Connected to MyHub3!
test
When I changed the first line to
const PoweredUP = require(".");
to make it use my self-compiled binary I get
node-poweredup$ node test.js
Looking for Hubs...
Connected to MyHub2!
Connected to MyHub3!
Of course this is only a partial answer because I still don't know why it compiles differently on my machine, but at least I have an idea where to start searching for the problem.

Running a test with Mocha also launches the main program

I'm trying to use Mocha to test a CLI app. The tests are running fine but, when I launch the testing procedure, it also launches the main app:
$ npm run test
> standardize-js#0.2.2 test C:\Users\Gaspard\Documents\Code\standardize-js
> mocha "./source/**/*.spec.js"
? Choose your project language or framework (Use arrow keys) //<-- THIS IS THE PROGRAM
> Javascript
Typescript
AngularJS
Main function //<-- THIS IS THE TEST
ask if the configuration is valid
Configuration is not valid, terminating program.
√ should return false if the configuration is not accepted
1 passing (29ms)
I'm kind of new to the testing world and I'm really struggling to understand what I'm doing wrong.
Here is the NPM script used to launch mocha :
"test": "mocha \"./source/**/*.spec.js\""
Here is my testing method:
/* eslint-disable func-names */
const { expect } = require("chai");
const main = require("./index").test;
describe("Main function", function() {
describe("ask if the configuration is valid", function() {
it("should return false if the configuration is not accepted", function() {
const fakeAnswer = false;
expect(main.validateConfiguration(fakeAnswer)).to.equal(false);
});
});
});
And here is my index.js file:
function validateConfiguration(answer) {
if (answer === false) {
console.log(chalk.red("Configuration is not valid, terminating program."));
return false;
}
return true;
}
const run = async () => {
//MAIN FUNCTION
};
run();
// Export functions and variables to be able to test
exports.test = {
validateConfiguration
};

It's not a problem with mocha. It is simply now node.js modules work.
When you do this:
const main = require("./index").test;
Node.js will execute index.js and then check the value of module.exports. If the module (index.js) sets or modifies module.exports then node will export it for use by require(). But note, in order for node to know that the module has exported anything it must execute the javascript file.
Node.js does not have any ability to parse and analyze javascript syntax (that's V8's job). Unlike other languages such as C or Java, modules in node.js are not implemented at the syntax level. Therefore the javascript language does not need to be modified (eg. ES6 modules) for node.js to support modules. Modules are simply implemented as a design pattern.
In your index.js file you call run:
run();
When require() loads index.js it will therefore also cause run() to be called.
Test libraries, not main
The solution to this is to implement your own logic as modules and test that, not test index.js:
mylib.js:
function validateConfiguration(answer) {
if (answer === false) {
console.log(chalk.red("Configuration is not valid, terminating program."));
return false;
}
return true;
}
// Export functions and variables to be able to test
exports.test = { validateConfiguration };
index.js:
const validateConfiguration = require("./mylib").test;
const run = async () => {
//MAIN FUNCTION
};
run();
You can now use your test script as written.
How can you not test code??
The strategy to keep index.js bug free without testing is to remove all logic from it except for the minimum amount of code to wire all your other code up together to run the app. The code should be as simple as "Hello World". That way, the code in main is so small and so simple that you can test it for bugs using your eyeballs.
Any code in index.js that causes a bug should be refactored into its own library so that it can be tested separately. There are a small handful of corner cases, such as loading environment variables or opening port 80 where you can't really separate into a library because they literally are wiring logic. For such cases you just have to be really careful.

It's calling run because you are telling it to right after defining the method.

"fetch is not found globally and no fetcher passed" when using spacejam in meteor

I'm writing unit tests to check my api. Before I merged my git test branch with my dev branch everything was fine, but then I started to get this error:
App running at: http://localhost:4096/
spacejam: meteor is ready
spacejam: spawning phantomjs
phantomjs: Running tests at http://localhost:4096/local using test-in-console
phantomjs: Error: fetch is not found globally and no fetcher passed, to fix pass a fetch for
your environment like https://www.npmjs.com/package/unfetch.
For example:
import fetch from 'unfetch';
import { createHttpLink } from 'apollo-link-http';
const link = createHttpLink({ uri: '/graphql', fetch: fetch });
Here's a part of my api.test.js file:
describe('GraphQL API for users', () => {
before(() => {
StubCollections.add([Meteor.users]);
StubCollections.stub();
});
after(() => {
StubCollections.restore();
});
it('should do the work', () => {
const x = 'hello';
expect(x).to.be.a('string');
});
});
The funniest thing is that I don't even have graphql in my tests (although, I use it in my meteor package)
Unfortunately, I didn't to find enough information (apart from apollo-link-http docs that has examples, but still puzzles me). I did try to use that example, but it didn't help and I still get the same error

I got the same error importing a npm module doing graphql queries into my React application. The app was compiling but tests were failing since window.fetch is not available in the Node.js runtime.
I solved the problem by installing node-fetch https://www.npmjs.com/package/node-fetch and adding the following declarations to jest.config.js:
const fetch = require('node-fetch')
global.fetch = fetch
global.window = global
global.Headers = fetch.Headers
global.Request = fetch.Request
global.Response = fetch.Response
global.location = { hostname: '' }
Doing so we instruct Jest on how to handle window.fetch when it executes frontend code in the Node.js runtime.

If you're using nodejs do the following:
Install node-fetch
npm install --save node-fetch
Add the line below to index.js:
global.fetch = require('node-fetch');

The problem is this: fetch is defined when you are in the browser, and is available as fetch, or even window.fetch
In the server it is not defined, and either needs to be imported explicity, or a polyfill like https://www.npmjs.com/package/unfetch (as suggested in the error message) needs to be imported by your test code to make the problem go away.

Mocking the filesystem in Jest tests

I'm writing up some tests for a graphics module and as part of those tests, I need a way to mock the fs module out in such a way that allows me to assert that data has been written to my fake file system and also to allow my fake file system to provide fake data back to test reading from the file system.
I'm aware that jest supports "manual mocks" where you create a static mock object as a file beside your code. Personally I would prefer to avoid this if at all possible and instead define my mock inline in my test files using jest.fn and/or jest.doMock.
Looking at the documentation, I feel like this should be possible and I feel like I'l about 75% there in asserting that my mocked fs.createWriteStream was called with 1 argument. I just can't seem to figure out how to assert that data was written to my mock fs.
I'm also aware that there are various mock-fs or similar modules available on npm. I would prefer to avoid these if possible and solve this entirely using the tools made available by jest.
Here is my test code thus far:
const fs = require('fs');
const pureimage = require('pureimage');
jest.mock('fs', () => ({
createWriteStream: jest.fn((file_name) => {
return file_name;
})
}));
describe('PNG image', () => {
it('can be encoded to a stream', () => {
const PImage = pureimage.make(200, 200);
const context = PImage.getContext('2d');
context.fillStyle = 'rgba(255,0,0, 0.5)';
context.fillRect(0, 0, 100, 100);
expect(pureimage.encodePNGToStream(PImage, fs.createWriteStream('myimage.png'))).resolves;
});
});
Full project can be found here: http://github.com/robertmain/node-pureimage

Replacing dependencies in AMD module format with testdouble.js

I'm writing tests for a JS application using Jasmine and testdouble.js as a mocking library. I am using AMD format to organize code in modules, and RequreJS as a module loader. I was wondering how to use testdouble.js to replace dependency for the module being tested that is in AMD format and it is loading via RequireJS. The documentation is unclear about this or I am missing something, so if someone could point me in the right direction.
I'll post the example bellow that illustrates my setup and the problem that I am facing.
car.js
define("car", ["engine"], function(engine) {
function drive = {
engine.run();
}
return {
drive: drive
}
});
engine.js
define("engine", function() {
function run() {
console.log("Engine running!");
}
return {
run: run
}
});
car.spec.js
define(["car"], function(car) {
describe("Car", function() {
it("should run the motor when driving", function() {
// I am not sure how to mock the engine's object run method
// and where to place that logic, in beforeEach or...
td.replace(engine, "run");
car.drive();
// How to verify that when car.run() has executed, it calls this mocked method
td.verify(engine.run());
});
});
});

testdouble.js does not have any explicit support for AMD modules. The only module-related tricks it offers are Node.js specific and built on top of Node's CJS module loader.
What you would need to do in this case is require from the test a reference to engine and replace the run property, which it seems like you've done (your example is incomplete).
If you do this, don't forget to run td.reset() in an afterEach to restore the original properties to anything you replace!