How to Test Through A Mocked Promise With Mocha?

Best Tools for Mocha Testing to Buy in October 2025

1

Express in Action: Writing, building, and testing Node.js applications

BUY & SAVE

$81.33

2

Test-Driving JavaScript Applications: Rapid, Confident, Maintainable Code

BUY & SAVE

$25.17 $38.00

Save 34%

3

Rails 5 Test Prescriptions: Build a Healthy Codebase

BUY & SAVE

$43.99 $47.95

Save 8%

4

BOOST Smart Water Bottle with Reminder & Tracker, Double Wall Vacuum Insulated Bottles Stainless Steel, 32oz BPA-Free Wide Mouth for Gym, Office, School - Ideal Gift,Mocha

• REWARD HYDRATION: EARN POINTS FOR EVERY SIP, REDEEM FOR DISCOUNTS!

• STAY ON TRACK: SMART REMINDERS PREVENT DEHYDRATION & BOOST WELLNESS GOALS.

• PRACTICAL DESIGN: LEAK-PROOF, EASY TO GRIP, AND EXCELLENT BATTERY LIFE!

BUY & SAVE

$54.99

5

UPGRADE Privacy Screen 5' x 25' Fence Commercial Shade Cover with Brass Grommets Heavy Duty Perfect for Outdoor Back Yard, Mocha, Customizable

• DURABLE HDPE MATERIAL: OFFERS LASTING STRENGTH AND WEATHER RESISTANCE.
• 90% BLACKOUT PRIVACY: ENSURES MAXIMUM SECLUSION AND UV PROTECTION.
• CUSTOMIZABLE OPTIONS: TAILOR SIZE, COLOR, AND DESIGN FOR YOUR NEEDS.

BUY & SAVE

$49.99

6

CHUANGHUI Car Door Handles for BMW X5 X6 F15 F16 2014-2018 Interior Door Handles Replace Cover Car Door Pull Handle Accessories (Mocha Brown)

• PREMIUM ABS+PC WITH TPU TREATMENT PREVENTS SCRATCHES AND WEAR.

• REVITALIZE YOUR BMW WITH OUR SLEEK, EASY-INSTALL DOOR HANDLE SET!

• PERFECT FIT FOR BMW X5 F15/F85 & X6 F16/F86 MODELS, 2014-2019.

BUY & SAVE

$42.99

7

CHUANGHUI Car Door Handle Cover for BMW 5 Series F10 2011-2016 Interior Door Handles Replace Trim Cover 520i 528i 530i 535d 535i 550i (Mocha Brown)

• PREMIUM ABS & TPU CONSTRUCTION: DURABLE, SCRATCH-RESISTANT FINISH.
• REVIVE YOUR INTERIOR: MAKE YOUR BMW LOOK BRAND NEW WITH EASY INSTALL.
• PERFECT FIT: CUSTOM-DESIGNED FOR BMW 5 SERIES F10 (2011-2016).

BUY & SAVE

$42.99

8

CHUANGHUI Car Door Handle for BMW X5 X6 E71 E70 2007-2013 Interior Door Handles Replace Cover Car Door Handle Accessories (Mocha Brown)

• PREMIUM ABS+PC & TPU: DURABLE, ANTI-SCRAPE DESIGN PROTECTS HANDLES.

• REVIVE YOUR CAR'S INTERIOR: INSTANTLY REFRESH AGED, WORN DOOR HANDLES.

• PERFECT FIT FOR BMW X5 E70/X6 E71: EASY 1:1 REPLACEMENT INSTALLATION.

BUY & SAVE

$36.79

9

CHUANGHUI Car Door Handle for BMW 5 Series F10 F11 2011-2016 Interior Door Handles Replace Cover Car Door Handle Assembly 520i 528i 530i 535d 535i 550i (Mocha Brown, Main Driver)

• PREMIUM ABS+PC WITH TPU TREATMENT FOR SUPERIOR SCRATCH RESISTANCE.

• REFRESH YOUR BMW 5 SERIES INTERIOR AND ENHANCE ITS APPEARANCE.

• 1:1 DESIGN ENSURES A PERFECT FIT FOR HASSLE-FREE INSTALLATION.

BUY & SAVE

$25.99

10

LARS NYSØM Stainless Steel Insulated Water Bottle 12oz 17oz 25oz 34oz 51oz | Insulated Thermo Flask for Hot and Cold Beverages | Leakproof Drinking Bottle (Mocha Brown, 1000ml)

• STYLISH & SUSTAINABLE: DITCH PLASTIC WITH OUR CHIC 34OZ STEEL BOTTLE.
• TRAVEL READY: LEAK-PROOF DESIGN ENSURES MESS-FREE HYDRATION ON THE GO.
• PERFECT GIFT IDEA: HIGH-QUALITY, BPA-FREE DESIGN IDEAL FOR ANY OCCASION.

BUY & SAVE

$28.99

+

ONE MORE?

In order to test through a mocked promise with Mocha, you can use a library like Sinon to create a fake promise object that you can manipulate. First, you would create a stub for the Promise object using Sinon's stub() method. This stub can be customized to return the values you want or simulate different scenarios.

Then, you would replace the actual promise in your code with this stub using dependency injection. This allows you to control the behavior of the promise and simulate different outcomes without making actual async calls.

Finally, in your Mocha test cases, you can test the different scenarios by calling the functions that use the promise and assert the expected behavior based on the stub's responses. This approach allows you to isolate and test the behavior of your code without relying on external dependencies, making your test more robust and predictable.

How to create custom assertions for testing mocked promises in mocha?

To create custom assertions for testing mocked promises in Mocha, you can follow these steps:

1. Create a new file for your custom assertions, for example, testUtils.js.
2. In this file, define your custom assertion function(s). For example, you can create a custom assertion function that checks if a promised value is equal to an expected value:

function assertPromisedValueEquals(promise, expected) { return promise.then(actual => { if (actual !== expected) { throw new Error(`Expected ${actual} to equal ${expected}`); } }); }

1. In your test file where you are testing mocked promises with Mocha, import your custom assertion function(s) at the top of the file:

const { assertPromisedValueEquals } = require('./testUtils');

1. Use your custom assertion function(s) in your test cases. For example:

it('should return the correct value', () => { const mockedPromise = Promise.resolve(42);

return assertPromisedValueEquals(mockedPromise, 42); });

1. Run your Mocha tests as usual. Your custom assertions will be used to check the outcomes of your mocked promises.

By creating custom assertions for testing mocked promises in Mocha, you can simplify your test cases and make them more readable and maintainable.

What are some best practices for testing through a mocked promise with mocha?

1. Use a testing framework like Mocha to create a test suite and assertions to verify that the promises are resolved/rejected as expected.
2. Use a mocking library like Sinon to create a mock promise object with the desired behavior (resolved/rejected) and return it when the function under test is called.
3. Use beforeEach and afterEach hooks in Mocha to create/setup the mocking behavior before and after each test case, ensuring clean state for each test.
4. Use .resolves and .rejects assertions provided by Chai to assert that the promise returned by the function under test is resolved or rejected with the expected value.
5. Use async/await or .then/.catch syntax to handle the promises returned by the function under test and verify the expected behavior.
6. Use sinon.stub or sinon.spy to track and verify the number of times the mocked function is called and what arguments it is called with.
7. Use sinon.restore to reset the mocked behavior after each test to ensure that subsequent tests are not affected by previous test cases.
8. Use sinon.useFakeTimers to simulate asynchronous behavior like timeouts or intervals when testing functions that rely on them.
9. Use sinon.useFakeXMLHttpRequest to mock HTTP requests and responses when testing functions that make AJAX calls.
10. Use sinon.fakeServer to create a fake server for more complex mocking of HTTP requests and responses in integration tests.

What are some examples of scenarios where a mocked promise would be useful in mocha testing?

1. Testing asynchronous code: A mocked promise can be used to simulate a function that returns a promise and ensure that the asynchronous code is being handled properly in the test.
2. Testing error handling: Mocked promises can be used to simulate different scenarios where a promise may be rejected, allowing for thorough testing of error handling within the code.
3. Simulating edge cases: Mocked promises can be used to simulate specific edge cases or unusual situations that may not occur frequently in the application but still need to be tested.
4. Testing complex sequences: Mocked promises can be used to test complex sequences of asynchronous operations, allowing the developer to set up specific scenarios and control the flow of the test.

How do you simulate different outcomes with a mocked promise in mocha?

You can simulate different outcomes with a mocked promise in Mocha by using a library like Sinon.js to create a fake promise object with specific behavior.

Here is an example of how you can use Sinon.js to mock a promise in a Mocha test:

const sinon = require('sinon');

describe('MyTestSuite', () => { it('should return resolved promise', async () => { const fakePromise = sinon.stub().resolves('Success');

// Call the function that returns a promise
const result = await fakePromise();

// Assertion
expect(result).to.equal('Success');

});

it('should return rejected promise', async () => { const fakePromise = sinon.stub().rejects(new Error('Failed'));

// Call the function that returns a promise
try {
  await fakePromise();
} catch (error) {
  // Assertion
  expect(error.message).to.equal('Failed');
}

}); });

In this example, we use Sinon.js to create a fake promise object that resolves with 'Success' for the first test case and rejects with an error for the second test case. We then call the fake promise in each test case and make assertions on the return values.

By using Sinon.js, you can easily simulate different outcomes with mocked promises in your Mocha tests.

How to test edge cases with a mocked promise in mocha testing?

To test edge cases with a mocked promise in Mocha testing, you can use the sinon library to mock the promise and its resolution or rejection. Here's a step-by-step guide on how to do this:

1. Install sinon library by running the following command in your project directory:

npm install sinon

1. In your test file, import sinon and any other necessary libraries:

const sinon = require('sinon');

1. Mock the promise using sinon.stub() method. For example, if you have a function that returns a promise, you can mock the promise like this:

const myFunction = require('./myFunction'); // import the function that returns a promise

describe('MyFunction', () => { it('should handle edge cases with a mocked promise', async () => { const mockedPromise = sinon.stub().resolves('mocked result'); // create a mock promise that resolves with a value const myFunctionStub = sinon.stub(myFunction, 'myAsyncFunction').returns(mockedPromise);

// Write your test logic here

sinon.assert.calledOnce(myFunctionStub); // ensure that the function was called with the stubbed promise

}); });

1. Write your test logic inside the test case, taking into account the edge cases you want to test. You can use sinon methods like calledOnce to assert that the mocked promise was called correctly.
2. Run your Mocha tests using the mocha command to verify that your edge cases are being handled correctly with the mocked promise.

By following these steps, you can effectively test edge cases with a mocked promise in Mocha testing using the sinon library.