React Basics~unit test/ui

• When I test current code, which is unit test, I use some tools. They are jest and react-testing-library.

・src/Example.js

import Greet from "./components/Greet";

const Example = () => {
  return <greet></greet>;
};

export default Example;

・src/component/Greet.jsx

const Greet = () => {
  return (
    <div>
      <form>
        <h1>Hello</h1>
        <input type="radio">
        <label htmlfor="fullname">Fullname</label>
        <input id="fullname" type="text" placeholder="Fullname">
        <button>button1</button>
        <button>button2</button>
        <img src="/static/imghwm/default1.png" data-src="/logo512.png" class="lazy" alt="React Logo">
        <h2>Hello2</h2>
      </form>
    </div>
  );
};

export default Greet;

・src/component/Greet.test.jsx

import { render, screen } from "@testing-library/react";
import Greet from "./Greet";

test("Whether elements exists or not", () => {
  const { debug, container } = render(<greet></greet>);
  //get the h1 element
  const h1El = screen.getByText("Hello");
  expect(h1El).toBeInTheDocument();

  //get the h2 element by specifying the name
  const headEl = screen.getByRole("heading", { name: "Hello2" });
  debug(headEl);
  expect(headEl).toBeInTheDocument();

  //get radio button
  const radioEl = screen.getByRole("radio");
  debug(radioEl);
  expect(radioEl).toBeInTheDocument();

  //get the img element
  const imgEl = screen.getByRole("img");
  debug(imgEl);
  expect(imgEl).toBeInTheDocument();

  //get the h1 element by getting the alt
  const imgEl2 = screen.getByAltText("React Logo");
  debug(imgEl2);
  expect(imgEl2).toBeInTheDocument();

  //get the h2 element by using the querySelector of container
  const h2El = container.querySelector("h2");
  debug(h2El);
  expect(h2El).toBeInTheDocument();

  //get an element by getting the labe
  const elByLabel = screen.getByLabelText("Fullname");
  debug(elByLabel);
  expect(elByLabel).toBeInTheDocument();

  //get an element by getting the placeholder
  const elByPlaceholder = screen.getByPlaceholderText("Fullname");
  debug(elByPlaceholder);
  expect(elByPlaceholder).toBeInTheDocument();
});

• The test function is a function of test.

• The first argument is a test title. The second argument is a callback function that executes the test code.

-In the callback function, I need to render a component that will be tested using a render function. And I can use debug and container if necessary.

const { debug, container } = render(<greet></greet>);

• And then, I need to get an element using screen.*.
  There are plenty of functions like getByText(), getByRole(), getByAltText() and so on.

• Finally, I need to know if the element exists in the document, using expect(element which I got before).toBeInTheDocument();.

• After writing the test code, I need to run this command npm test.

・Success(The taest passed)

・Failure(The taest failed)

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