Testing Stimulus Controllers

// hello_controller.test.js
import { Application as StimulusApp } from "stimulus";
import HelloController from "path/to/js/hello_controller";

describe("HelloController", () => {
  beforeEach(() => {
    // Insert the HTML and register the controller
    document.body.innerHTML = `
      <div data-controller="hello">
        <input data-target="hello.name" type="text">
        <button data-action="click->hello#greet">
          Greet
        </button>
        <span data-target="hello.output">
        </span>
      </div>
    `;
    StimulusApp.start().register('hello', HelloController);
  })

  it("inserts a greeting using the name given", () => {
    const helloOutput =  document.querySelector("[data-target='hello.output']");
    const nameInput = document.querySelector("[data-target='hello.name']");
    const greetButton = document.querySelector("button");
    // Change the input value and click the greet button
    nameInput.value = "Laurence";
    greetButton.click();
    // Check we have the correct greeting
    expect(helloOutput).toHaveTextContent("Hello, Laurence!");
  })
})