How do I mock a specific function from a module for a specific test (Jest) - testing

Question

I have an api.js file that contains my api call. It looks like this:
// api.js
// reusable fetch call
export const makeFetch = async (url, options) => {
try {
const response = await fetch(url, options);
if (!response.ok) {
throw new Error(`${response.status}`);
}
return await response.json();
} catch (error) {
throw new Error(`Network request failed. (error: ${error.message})`);
}
};
// actual fetch call
export const getCards = async () => {
const url = 'http://localhost:3001/api/v1/cards';
return await makeFetch(url);
};
Then I have an api.test.js file that looks like:
//api.test.js
import { makeFetch, getCards } from './api';
describe('makeFetch', () => {
// three successful tests
});
// this is where I have issues
describe('getCards', () => {
it('calls makeFetch', async () => {
await getCards();
expect(makeFetch).toHaveBeenCalledTimes(1);
});
});
this is the error I get:
FAIL src\api\api.test.js
● getCards › calls makeFetch
ReferenceError: makeFetch is not defined
at Object.it.only (src/api/api.test.js:51:15)
at new Promise (<anonymous>)
at Promise.resolve.then.el (node_modules/p-map/index.js:46:16)
at <anonymous>
at process._tickCallback (internal/process/next_tick.js:182:7)
Does anyone know how to make this pass with making my previous tests fail? Thank you for your time.

Answer 1

You need to create a mock of makeFetch. You can do that using spyOn and mockReturnValue.
You will need to move makeFetch into its own file (lib.js) so that you can mock and replace it in your test:
// ---- lib.js ----
// reusable fetch call
export const makeFetch = async (url, options) => {
try {
const response = await fetch(url, options);
if (!response.ok) {
throw new Error(`${response.status}`);
}
return await response.json();
} catch (error) {
throw new Error(`Network request failed. (error: ${error.message})`);
}
};
// ---- api.js ----
import { makeFetch } from './lib';
// actual fetch call
export const getCards = async () => {
const url = 'http://localhost:3001/api/v1/cards';
return await makeFetch(url);
};
// ---- api.test.js ----
import * as lib from './lib';
import { getCards } from './api';
describe('makeFetch', () => {
// three successful tests
});
describe('getCards', () => {
it('calls makeFetch', async () => {
const simulatedResponse = { data: 'simulated response' };
// mock makeFetch
const mock = jest.spyOn(lib, 'makeFetch');
mock.mockReturnValue(Promise.resolve(simulatedResponse));
const result = await getCards();
expect(result).toEqual(simulatedResponse);
expect(mock).toHaveBeenCalledTimes(1);
expect(mock).toHaveBeenCalledWith('http://localhost:3001/api/v1/cards');
// restore makeFetch
mock.mockRestore();
});
});