Testing mousedown event outside React Component: Jest + Enzyme

Question

I want write a test using Jest and Enzyme that tests a component that has an event listener, such that when a mousedown event occurs outside of a given html element, a change occurs (in this example, a state value is toggled). I am using jest to mock the event listener and simulate the mousedown event, however, when I try to run this test, I am getting the following error message:

TypeError: Failed to execute 'contains' on 'Node': parameter 1 is not of type 'Node'.

Obviously I think that <div /> is not the right value I should be providing when I simulate my mousedown event with map.mousedown({ target: <section /> }); . How do I properly simulate a mousedown event that occurs outside of my component? You can see the code below. Thanks!

sampleComponent.jsx:

import * as React from 'react';

const SampleComponent = () => {
  const [state, setState] = React.useState(false);
  const ref = React.useRef(null);

  const handleClickOutside = (event) => {
    if (
      !ref.current.contains(event.target)
    ) {
      setState(true);
    }
  };

  React.useEffect(() => {
    document.addEventListener('mousedown', handleClickOutside);
    return () => document.removeEventListener('mousedown', handleClickOutside);
  });

  return (
    <div
      id="sample-div"
      ref={ref}
    >
      {`State value is: ${state}`}
    </div>
  );
};

export default SampleComponent;

sampleComponent.test.jsx:

import * as React from 'react';
import { mount } from 'enzyme';
import SampleComponent from './sampleComponent';

const setup = () => mount(<SampleComponent />);

test('testing mousedown', () => {
  const map = {};
  document.addEventListener = jest.fn((event, callback) => {
    map[event] = callback;
  });
  const wrapper = setup();
  expect(wrapper.find('#sample-div').text()).toBe('State value is: false');
  map.mousedown({ target: <section /> });
  expect(wrapper.find('#sample-div').text()).toBe('State value is: true');
});

Answer 1

You can't pass react JSX as the value of event.target . Since you use document.addEventListener , it's native DOM event. You need pass a native DOM, like document.createElement('a') .

Here is the tests cases for your example:

sampleComponent.tsx :

import React from 'react';

const SampleComponent = () => {
  const [state, setState] = React.useState(false);
  const ref = React.useRef(null);

  const handleClickOutside = event => {
    if (!(ref.current as any).contains(event.target)) {
      setState(true);
    }
  };

  React.useEffect(() => {
    document.addEventListener('mousedown', handleClickOutside);
    return () => document.removeEventListener('mousedown', handleClickOutside);
  });

  return (
    <div id="sample-div" ref={ref}>
      {`State value is: ${state}`}
    </div>
  );
};

export default SampleComponent;

sampleComponent.test.tsx :

import React from 'react';
import { mount } from 'enzyme';
import SampleComponent from './sampleComponent';
import { act } from 'react-dom/test-utils';

const setup = () => mount(<SampleComponent />);

beforeEach(() => {
  jest.resetAllMocks();
});
test('testing mousedown - 1', () => {
  const map: any = {};
  document.addEventListener = jest.fn((event, callback) => {
    map[event] = callback;
  });
  const wrapper = setup();
  expect(wrapper.find('#sample-div').text()).toBe('State value is: false');
  act(() => {
    map.mousedown({ target: document.createElement('a') });
  });
  expect(wrapper.find('#sample-div').text()).toBe('State value is: true');
  expect(document.addEventListener).toBeCalledTimes(2);
});

test('testing mousedown - 2', () => {
  const map: any = {};
  document.addEventListener = jest.fn((event, callback) => {
    map[event] = callback;
  });
  const wrapper = setup();
  expect(wrapper.find('#sample-div').text()).toBe('State value is: false');
  act(() => {
    map.mousedown({ target: wrapper.getDOMNode() });
  });
  expect(wrapper.find('#sample-div').text()).toBe('State value is: false');
  expect(document.addEventListener).toBeCalledTimes(1);
});

Unit test result with 100% coverage:

PASS  src/stackoverflow/58610112/sampleComponent.test.tsx (8.041s)
  ✓ testing mousedown - 1 (46ms)
  ✓ testing mousedown - 2 (3ms)

---------------------|----------|----------|----------|----------|-------------------|
File                 |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
---------------------|----------|----------|----------|----------|-------------------|
All files            |      100 |      100 |      100 |      100 |                   |
 sampleComponent.tsx |      100 |      100 |      100 |      100 |                   |
---------------------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        9.5s