How to Test stopPropagation() in React Testing Library

Introduction: Testing stopPropagation() in React

Correctly implementing stopPropagation() is vital when dealing with nested click events in React. Instead of directly verifying stopPropagation()'s call, focus on testing its outcome: does the event propagate or not?

This article compares two approaches:

✅ Testing the effect of stopPropagation() (event propagation).

✅ Mocking the stopPropagation() method.

✅ Determining which method is superior and when to use each.

Best Approach: Testing Event Propagation

The optimal method tests stopPropagation()'s effect by wrapping the component within a parent <div> with an <code>onClick handler. We then check if the event bubbles up to the parent.

Example: Preventing Propagation

import { render, screen } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
import { FormElementsList } from "@/components/FormElementsList";

it("prevents event propagation on click", async () => {
  const onOuterClick = jest.fn();

  render(
    <div onClick={onOuterClick}>
      <FormElementsList />
    </div>
  );

  const textInputElement = screen.getByText("Text Input");
  await userEvent.click(textInputElement);

  expect(onOuterClick).toHaveBeenCalledTimes(0); // Event propagation prevented
});

Why This Works:

1. The parent <div>'s <code>onClick handler (onOuterClick) acts as a listener.
2. If stopPropagation() functions correctly within FormElementsList, clicking an element shouldn't trigger onOuterClick.
3. expect(onOuterClick).toHaveBeenCalledTimes(0) confirms successful event prevention.

Alternative: Mocking stopPropagation()

Alternatively, you can directly verify stopPropagation()'s call by mocking the event and tracking the function call.

Example: Mocking stopPropagation()

import { render, screen } from "@testing-library/react";
import { FormElementsList } from "@/components/FormElementsList";

it("calls stopPropagation() on click", async () => {
  render(<FormElementsList />);

  const textInputElement = screen.getByText("Text Input");

  const event = new MouseEvent("click", { bubbles: true });
  jest.spyOn(event, "stopPropagation");

  textInputElement.dispatchEvent(event);

  expect(event.stopPropagation).toHaveBeenCalled();
});

Why This Works:

• jest.spyOn(event, "stopPropagation") monitors the function call.
• dispatchEvent(event) manually triggers the click.
• expect(event.stopPropagation).toHaveBeenCalled() ensures stopPropagation()'s execution.

Choosing the Right Method

Method

Pros

Cons

Testing Event Propagation

Tests actual user behavior

Doesn't directly confirm
Method	Pros	Cons
Testing Event Propagation	Tests actual user behavior	Doesn't directly confirm stopPropagation() call
Mocking stopPropagation()	Directly confirms stopPropagation() call	Tests implementation, not behavior
call
Mocking

Directly confirms call

Tests implementation, not behavior

RecommendationstopPropagation()

Prioritize testing real behavior over implementation details for better maintainability. The event propagation method is generally preferred. Use mocking only when absolutely necessary to verify the specific call to .