React Basics~unit test/custom hook

• When I test a custom hook component, I use a renderHook imported from @testing-library/react' and an act imported fromreact-dom/test-utils'.

・src/App.tsx

import "./App.css";
import Counter from "./component/counter/Counter";

function App() {
  return (
    <div className="App">
      <Counter />
    </div>
  );
}

export default App;

・src/component/counter/Counter.tsx

import React, { useState } from "react";
import { useCounter } from "../../hooks/useCounter";

const Counter = () => {
const { count, increment } = useCounter({ initialCount: 10 });

  return (
    <div>
      <h1>{count}</h1>
      <button onClick={() => increment()}>Increment</button>
    </div>
  );
};

export default Counter;

・src/hooks/useCounter.tsx

import React, { useState } from "react";
import { UseCounterProps } from "./useCounter.type";

type UseCounterProps = {
  initialCount?: number;
};


export const useCounter = ({ initialCount = 0 }: UseCounterProps = {}) => {
  const [count, setCount] = useState(initialCount);
  const increment = () => setCount((prev) => prev + 1);

  return { count, increment };
};

・src/hooks/useCounter.test.tsx

import { renderHook } from "@testing-library/react";
import { useCounter } from "./useCounter";
import { act } from "react-dom/test-utils";

describe("useCounter", () => {
  test("Should render the initial count", () => {
    const { result } = renderHook(useCounter, {
      initialProps: { initialCount: 10 },
    });
    expect(result.current.count).toBe(10);
  });

  test("Increment the  count", () => {
    const { result } = renderHook(useCounter);
    act(() => {
      result.current.increment();
    });
    expect(result.current.count).toBe(1);
  });
});

• When I pass a props, in this case it is initialCount(=10), I add a property which is initialProps: { initialCount: 10 }.

• When I test a function of the custom hook, in this case the increment(), I use the act and call the increment() inside the callback.

・Success

・Failure

・the display action