An example of Counter in React with two different testing tools

counter-enzyme.test.js

import React from "react";
import { shallow } from "enzyme";

import Counter from "./counter";

describe("<Counter />", () => {
  it("properly increments and decrements the counter", () => {
    const wrapper = shallow(<Counter />);
    expect(wrapper.state("count")).toBe(0);

    wrapper.instance().increment();
    expect(wrapper.state("count")).toBe(1);

    wrapper.instance().decrement();
    expect(wrapper.state("count")).toBe(0);
  });
});

counter-rtl.test.js

import React from "react";
import { fireEvent, render, screen } from "@testing-library/react";

import Counter from "./counter";

describe("<Counter />", () => {
  it("properly increments and decrements the counter", () => {
    render(<Counter />);
    const counter = screen.getByText("0");
    const incrementButton = screen.getByText("+");
    const decrementButton = screen.getByText("-");

    fireEvent.click(incrementButton);
    screen.getByText("1");

    fireEvent.click(decrementButton);
    screen.getByText("0");
  });
});

counter.js

import React from "react"

class Counter extends React.Component {
  state = { count: 0 }
  increment = () => this.setState(({ count }) => ({ count: count + 1 }))
  decrement = () => this.setState(({ count }) => ({ count: count - 1 }))
  render() {
    return (
      <div>
        <button onClick={this.decrement}>-</button>
        <p>{this.state.count}</p>
        <button onClick={this.increment}>+</button>
      </div>
    )
  }
}

export default Counter