I want to test history.push in jest

Question

I am a beginner in testing.

I am writing a test using jest and enzyme. However, when I tried to write a test for history.push(), I got the following error.

TypeError: Cannot read property 'pathname' of undefined.

Here is my test code and the component code.

export default function Tags() {
  const classes = useStyles();
  const history = useHistory();

  const isSelected = (category: string) => {
    history.push(`/?category=${category}`);
  };

  return (
    <>
      <List className={classes.root} aria-label="contacts">
        <ListItem button onClick={() => isSelected("backend")}>
          <ListItemText primary="#backend" id="backend" />
        </ListItem>
        <ListItem button onClick={() => isSelected("frontend")}>
          <ListItemText primary="#frontend" id="frontend" />
        </ListItem>
      </List>
    </>
  );
}

import * as React from "react";
import ReactDOM, * as ReactDom from "react-dom";
import Tags from "../Tags";
import { configure, mount, shallow } from "enzyme";
import Adapter from "enzyme-adapter-react-16";
import { fireEvent } from "@testing-library/react";
import { useHistory } from "react-router-dom";

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

jest.mock("react-router-dom", () => ({
  useHistory: (): any => ({
    push: jest.fn(),
  }),
}));

describe("Tags", () => {
  it("should be pushed correct path", () => {
    const wrapper = mount(<Tags />);
    const history: any = useHistory();
    const backend = wrapper.find("div#backend").getDOMNode();
    fireEvent.click(backend);
    expect(history.location.pathname).toBe("?category=backend");
  });
});

What I want to achieve is if I click on the button, it will access the correct url or not.

I don't know where and how to rewrite the code to make the test work. Can you please tell me how to do this?

Answer 1

Update: Mocking useHistory is not recommended anymore. Instead, we should use <MemoryRouter initialEntries={['/']}/> or createMemoryHistory, see https://testing-library.com/docs/example-react-router/

You can do this:

Tags.tsx:

import { useHistory } from "react-router-dom";
import React from "react";

export default function Tags() {
  const history = useHistory();

  const isSelected = (category: string) => {
    history.push(`/?category=${category}`);
  };

  return (
    <>
      <ul aria-label="contacts">
        <li id="backend" onClick={() => isSelected("backend")}></li>
        <li id="frontend" onClick={() => isSelected("frontend")}></li>
      </ul>
    </>
  );
}

Tags.test.tsx:

import React from "react";
import Tags from "./Tags";
import { mount } from "enzyme";
import ReactRouterDom from "react-router-dom";

const mHistory = {
  push: jest.fn(),
};

jest.mock("react-router-dom", () => ({
  ...(jest.requireActual("react-router-dom") as typeof ReactRouterDom),
  useHistory: jest.fn(() => mHistory),
}));

describe("Tags", () => {
  afterAll(() => {
    jest.resetAllMocks();
  });
  it("should be pushed correct path", () => {
    const wrapper = mount(<Tags />);
    const backend = wrapper.find("#backend");
    backend.simulate("click");
    expect(mHistory.push).toBeCalledWith("/?category=backend");
  });
});

unit test result:

 PASS  examples/65245622/Tags.test.tsx
  Tags
    ✓ should be pushed correct path (33 ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |   88.89 |      100 |      75 |   88.89 |                   
 Tags.tsx |   88.89 |      100 |      75 |   88.89 | 15                
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        6.056 s

source code: https://github.com/mrdulin/jest-v26-codelab/tree/main/examples/65245622