How do I mock a async function in a component when testing reactjs with enzyme and jest?

Question

I have a TextField (named EmailTextField) of which is used to enter e-mail address. When user enters email address and 'onBlur' event is occur, I have a async function named 'verifyUserNameAvailable' to make api call to server and check if email address is already taken or not.

Now, I want to create a unit test for this TextField. I do not want to test the 'verifyUserNameAvailable' as I already have a test for that in different test suite. Is there a way to mock

const response = await verifyUserNameAvailable(emailAddress);

call in handleOnBlur function?

ex. I want to unit test EmailTextField when response is 'true' and response is 'false'.

EmailTextField component

import React, {useRef, useState} from 'react';
import TextField from "@material-ui/core/TextField";
import Grid from "@material-ui/core/Grid";
import {verifyUserNameAvailable} from "../../../../api/auth/authApiConsumer";

export const EmailTextField = props => {

  const {onStateChange} = props;
  const [state, setState] = useState({
    errors: [],
    onChange: false,
    pristine: false,
    touched: false,
    inProgress: false,
    value: {
      email: '',
    },
  });
  const [currentReq, setCurrentReq] = useState(0);
  const latestReq = useRef(currentReq);

  const helperText = 'Email address will be used as your account id';
  const helperTextPristine = "'" + state.value.email + "' is available.";

  const handleOnBlur = async (event) => {

  const emailAddress = String(event.target.value).toLowerCase();



  // If true, verify username is available
  const updatedState = {
    ...state,
    touched: true,
    pristine: false,
    value: {
      email: emailAddress,
    },
    inProgress: true
  };
  setState(updatedState);
  onStateChange(updatedState);


  const response = await verifyUserNameAvailable(emailAddress);


  if (response === true) {

    const updatedState = {
      ...state,
      touched: true,
      pristine: true,
      value: {
        email: emailAddress,
      },
      inProgress: false,
      errors: [],
    };
    setState(updatedState);
    onStateChange(updatedState);

  } else {

    const updatedState = {
      ...state,
      touched: true,
      pristine: false,
      value: {
        email: emailAddress,
      },
      inProgress: false,
      errors: ["'" + emailAddress + "' is already used."],
    };
    setState(updatedState);
    onStateChange(updatedState);

  }

  };

  return (
      <Grid container spacing={1}>
        <Grid item xs={12}>
          <TextField
              variant="outlined"
              required
              fullWidth
              id="email"
              label="email address"
              error={state.errors.length > 0}
              helperText={state.errors.length > 0 ? state.errors[0]
                  : state.pristine === true ? helperTextPristine : helperText}
              name="email"
              autoComplete="email"
              margin='dense'
              onBlur={handleOnBlur}
          />
        </Grid>
      </Grid>
  )

};

export default EmailTextField;

Below is a unit test that I want to create.


import React from 'react';
import {configure} from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';
import EmailTextField from './EmailTextField';
import TextField from '@material-ui/core/TextField';
import {createShallow} from '@material-ui/core/test-utils';
import {act} from 'react-dom/test-utils';

configure({adapter: new Adapter()});

describe('<EmailTextField />', () => {
  let shallow;

  beforeAll(() => {
    shallow = createShallow();
  });
  let wrapper;
  beforeEach(() => {
    wrapper = shallow(<EmailTextField onStateChange={handleStateChange}/>);
  });

  const handleStateChange = jest.fn()


  it('should show error when already registered account is entered', () => {

    // MOCK - Not a working code here.. but I want to do something like...
    when(verifyUserNameAvailable).isCalledReturn(false);
    ////////////////////////

    act(() => {
      wrapper.find(TextField).at(0).simulate('blur', {target: {value: '[email protected]'}});
    });
    wrapper.update();
    expect(wrapper.find(TextField).at(0).props().error).toBe(
        true);
    expect(wrapper.find(TextField).at(0).props().helperText).toBe(
        "[email protected] is already used.");
    expect(handleStateChange).toHaveBeenCalledWith({
      "errors": ["[email protected] is already used."],
      "inProgress": false,
      "onChange": false,
      "pristine": false,
      "touched": true,
      "value": {"email": "[email protected]"}
    });
  });

  it('should not show error when account is not previously registered', () => {

    // MOCK - Not a working code here.. but I want to do something like...
    when(verifyUserNameAvailable).isCalledReturn(true);
    ////////////////////////

    act(() => {
      wrapper.find(TextField).at(0).simulate('blur', {target: {value: '[email protected]'}});
    });
    wrapper.update();
    expect(wrapper.find(TextField).at(0).props().error).toBe(
        true);
    expect(wrapper.find(TextField).at(0).props().helperText).toBe(
        "[email protected] is available.");
    expect(handleStateChange).toHaveBeenCalledWith({
      "errors": ["[email protected] is available."],
      "inProgress": false,
      "onChange": false,
      "pristine": true,
      "touched": true,
      "value": {"email": "[email protected]"}
    });
  });

});

Is there a way to do something like this in above?

// MOCK - Not a working code here.. but I want to do something like...
when(verifyUserNameAvailable).isCalledReturn(true);
////////////////////////

update

I tried to create a mock under ../../../../api/auth/__mocks__/authApiConsumer

export const verifyUserNameAvailable = (email) => new Promise(
    function (resolve, reject) {
     resolve(true);
    });

and updated the unit test to look like


import React from 'react';
import {configure} from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';
import EmailTextField from './EmailTextField';
import TextField from '@material-ui/core/TextField';
import {createShallow} from '@material-ui/core/test-utils';
import {act} from 'react-dom/test-utils';

jest.mock("../../../../api/auth/authApiConsumer");

configure({adapter: new Adapter()});

describe('<EmailTextField />', () => {
  let shallow;

  beforeAll(() => {
    shallow = createShallow();
  });
  let wrapper;
  beforeEach(() => {
    wrapper = shallow(<EmailTextField onStateChange={handleStateChange}/>);
  });

  const handleStateChange = jest.fn()


  it('should not show error when account is not previously registered', () => {

    act(() => {
      wrapper.find(TextField).at(0).simulate('blur', {target: {value: '[email protected]'}});
    });
    wrapper.update();
    expect(wrapper.find(TextField).at(0).props().error).toBe(
        true);
    expect(wrapper.find(TextField).at(0).props().helperText).toBe(
        "[email protected] is available.");
    expect(handleStateChange).toHaveBeenCalledWith({
      "errors": ["[email protected] is available."],
      "inProgress": false,
      "onChange": false,
      "pristine": true,
      "touched": true,
      "value": {"email": "[email protected]"}
    });
  });

});

But this does not work...

Looks like the mock function I created is being ignored or something..

Darko Vasilev · Accepted Answer · 2019-07-24 10:21:11Z

1

You need to run the test in the next tick. Try this code. It works fine.

import React from 'react';
import { configure } from "enzyme";
import Adapter from "enzyme-adapter-react-16";
import EmailTextField from "./EmailTextField";
import TextField from "@material-ui/core/TextField";
import { createShallow } from "@material-ui/core/test-utils";
import { act } from "react-dom/test-utils";


jest.mock('./api/authApiConsumer');
const MOCK_MAIL = "[email protected]";

configure({ adapter: new Adapter() });

describe("<EmailTextField />", () => {
    const handleStateChange = jest.fn();
    let shallow;

    beforeAll(() => {
        shallow = createShallow();
    });
    let wrapper;
    it("should work", () => {
        wrapper = shallow(
            <EmailTextField onStateChange={handleStateChange} />
        );
    });

    it("should not show error when account is not previously registered", (done) => {
        act(() => {
            wrapper.find(TextField).at(0).simulate('blur', { target: { value: '[email protected]' } });
        });
        process.nextTick(() => {
            wrapper.update();
            expect(
                wrapper
                    .find(TextField)
                    .at(0)
                    .props().error
            ).toBe(false);
            expect(
                wrapper
                    .find(TextField)
                    .at(0)
                    .props().helperText
            ).toBe(`'${MOCK_MAIL}' is available.`);
            expect(handleStateChange).toHaveBeenCalledWith({
                errors: [],
                inProgress: false,
                onChange: false,
                pristine: true,
                touched: true,
                value: { email: MOCK_MAIL }
            });
            done();

        })
    });
});

answered Jul 24, 2019 at 10:21

Darko Vasilev

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2 Comments

Darko Vasilev Over a year ago

you need to change the jest mock path.

hinewwiner Over a year ago

This works! Thanks very much. I am not sure how the nextTick work but I will need to play with it for a while. Thank you very much!

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