I have a simple React application with the following App.js, App.test.js, and utils.js files:
App.js
import React from 'react';
import { randomNameGenerator } from './utils.js';
import './App.css';
function App() {
return (
<div>
{randomNameGenerator()}
</div>
);
}
export default App;
App.test.js
import React from 'react';
import { render } from '@testing-library/react';
import '@testing-library/jest-dom/extend-expect'
import App from './App';
it('allows Jest method mocking', () => {
const { getByText } = render(<App />);
expect(getByText("Craig")).toBeInTheDocument()
});
utils.js
export function randomNameGenerator() {
return Math.floor((Math.random() * 2) + 1) == 1 ? 'Steve' : 'Bill';
}
This is a simple example, but what I'm trying to acplish is a Jest mock of the randomNameGenerator() function to only return "Craig" for that specific Jest test.
I've followed a wide variety of tutorials/guides, but can't find anything that works - the closest (by "feel") that I've gotten was this (in App.test.js), which had no effect:
jest.doMock('./utils', () => {
const originalUtils = jest.requireActual('./utils');
return {
__esModule: true,
...originalUtils,
randomNameGenerator: jest.fn(() => {
console.log('## Returning mocked typing duration!');
return 'Craig';
}),
};
})
The way it fails is expected:
Unable to find an element with the text: Craig. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible.
<body>
<div>
<div>
Steve
</div>
</div>
</body>
6 | it('allows Jest method mocking', () => {
7 | const { getByText } = render(<App />);
> 8 | expect(getByText("Craig")).toBeInTheDocument()
| ^
9 | });
I have a simple React application with the following App.js, App.test.js, and utils.js files:
App.js
import React from 'react';
import { randomNameGenerator } from './utils.js';
import './App.css';
function App() {
return (
<div>
{randomNameGenerator()}
</div>
);
}
export default App;
App.test.js
import React from 'react';
import { render } from '@testing-library/react';
import '@testing-library/jest-dom/extend-expect'
import App from './App';
it('allows Jest method mocking', () => {
const { getByText } = render(<App />);
expect(getByText("Craig")).toBeInTheDocument()
});
utils.js
export function randomNameGenerator() {
return Math.floor((Math.random() * 2) + 1) == 1 ? 'Steve' : 'Bill';
}
This is a simple example, but what I'm trying to acplish is a Jest mock of the randomNameGenerator() function to only return "Craig" for that specific Jest test.
I've followed a wide variety of tutorials/guides, but can't find anything that works - the closest (by "feel") that I've gotten was this (in App.test.js), which had no effect:
jest.doMock('./utils', () => {
const originalUtils = jest.requireActual('./utils');
return {
__esModule: true,
...originalUtils,
randomNameGenerator: jest.fn(() => {
console.log('## Returning mocked typing duration!');
return 'Craig';
}),
};
})
The way it fails is expected:
Unable to find an element with the text: Craig. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible.
<body>
<div>
<div>
Steve
</div>
</div>
</body>
6 | it('allows Jest method mocking', () => {
7 | const { getByText } = render(<App />);
> 8 | expect(getByText("Craig")).toBeInTheDocument()
| ^
9 | });
1 Answer
Reset to default 9You can mock the module by calling jest.mock, and then import it, then inside your tests you call mockImplementation to setup the right return value.
import React from 'react';
import { render } from '@testing-library/react';
import '@testing-library/jest-dom/extend-expect'
import App from './App';
import { randomNameGenerator } from "./utils";
jest.mock('./utils.js', () => ({
randomNameGenerator: jest.fn()
}));
describe('test', () => {
it('allows Jest method mocking 1', () => {
randomNameGenerator.mockImplementation(() => "Craig");
const { getByText } = render(<App />);
expect(getByText("Craig")).toBeInTheDocument()
});
it('allows Jest method mocking 2', () => {
randomNameGenerator.mockImplementation(() => "Not Craig");
const { getByText } = render(<App />);
expect(getByText("Not Craig")).toBeInTheDocument()
});
});