Testing async code in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an async function.

Node.js

async function fetchData() {
  const data = await [1]();
  return data;
}

Drag options to blanks, or click blank then click option'

AloadData

BfetchData

CgetData

DretrieveData

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-async function with await causes errors.

Calling a function that does not return a promise.

The await keyword waits for the promise returned by getData() to resolve.

2fill in blank

medium

Complete the code to test an async function using Jest.

Node.js

test('fetchData returns data', async () => {
  const data = await fetchData();
  expect(data).[1]('value');
});

Drag options to blanks, or click blank then click option'

AtoBe

BtoEqual

CtoContain

DtoHaveLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using toBe for object comparison causes test failures.

Forgetting to use async/await in the test function.

toEqual checks that the returned data matches the expected value deeply.

3fill in blank

hard

Fix the error in the async test by completing the code.

Node.js

test('fetchData throws error', async () => {
  await expect(fetchData()).[1]();
});

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Arejects.toThrow

Bresolves.toThrow

Cresolves.toBe

Drejects.toBe

Attempts:

3 left

💡 Hint

Common Mistakes

Using resolves when expecting an error causes false positives.

Not awaiting the expect call leads to unhandled promise rejections.

Use rejects.toThrow to test that a promise rejects with an error.

4fill in blank

hard

Fill both blanks to correctly mock an async function with Jest.

Node.js

jest.mock('./api');
const api = require('./api');

api.fetchData = jest.fn().[1](() => Promise.[2]('mocked data'));

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AmockImplementation

BmockResolvedValue

Cresolve

DmockRejectedValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using mockRejectedValue when expecting success.

Using mockImplementation without returning a promise.

mockImplementation with Promise.resolve mocks a promise that resolves with the given value.

5fill in blank

hard

Fill all three blanks to write a complete async test with setup and teardown.

Node.js

beforeEach(() => {
  jest.[1]();
});

afterEach(() => {
  jest.[2]();
});

test('async fetchData test', async () => {
  const data = await fetchData();
  expect(data).[3]('result');
});

Drag options to blanks, or click blank then click option'

AclearAllMocks

BresetAllMocks

CtoContain

DtoBe

Attempts:

3 left

💡 Hint

Common Mistakes

Not clearing mocks before tests causes interference.

Using toBe when checking for substring presence.

clearAllMocks clears mock calls before each test, resetAllMocks resets mock states after each test, and toContain checks if the result includes a value.