React Testing: Avoid implementation details

🧪 Avoiding Implementation Details in Your React Tests

When writing tests for your React components, there’s one golden rule that can make your code more robust, flexible, and maintainable:

✅ Don’t test implementation details. ❌ Test what the user sees and does.

Let’s break down what that means, why it matters, and how to fix tests that break unnecessarily when you refactor your components.

💭 What Are Implementation Details?

Implementation details are the internal workings of your code — how an outcome is achieved. In contrast, public behavior is what the end user sees or interacts with.

Here’s an example with a simple utility function:

multiply(4, 5) // 20

The implementation of multiply() could be anything:

const multiply = (a, b) => a * b

Or even:

function multiply(a, b) {
  let total = 0
  for (let i = 0; i < b; i++) {
    total += a
  }
  return total
}

The point? The user doesn’t care how you got the result — just that it’s correct.

Now let’s apply this principle to React component testing.

🚨 A Real Testing Problem

Here’s a simple Counter component:

function Counter() {
  const [count, setCount] = React.useState(0)
  const increment = () => setCount(c => c + 1)
  return <button onClick={increment}>{count}</button>
}

In our test, we might do this:

const { container } = render(<Counter />)
fireEvent.click(container.firstChild)
expect(container.firstChild.textContent).toBe('1')

But what if we refactor?

function Counter() {
  const [count, setCount] = React.useState(0)
  const increment = () => setCount(c => c + 1)
  return (
    <span>
      <button onClick={increment}>{count}</button>
    </span>
  )
}

💥 Boom. The test fails — even though the component works just fine for the user. Why? Because we wrote the test based on the component’s structure — an implementation detail.

✅ How to Test the Right Way

Let’s fix that using React Testing Library’s user-centric queries.

import { render, screen, fireEvent } from '@testing-library/react'
import Counter from '../counter'

test('increments the counter', () => {
  render(<Counter />)

  const button = screen.getByRole('button', { name: '0' })
  fireEvent.click(button)

  expect(button).toHaveTextContent('1')
})

Why This Is Better:

• ✅ screen.getByRole('button', { name: '0' }) matches how users experience the UI
• ✅ Doesn’t rely on specific tag structure or DOM tree
• ✅ Won’t break if we wrap elements or change HTML tags
• ✅ Easy to refactor your component without rewriting tests

📚 Learn more about screen: https://testing-library.com/docs/dom-testing-library/api-queries#screen

💯 Bonus: Simulate Events Like a Real User

Even calling fireEvent.click(button) isn’t quite how users interact. When a user clicks a button, they:

• Hover over it
• Focus it
• Mouse down
• Mouse up
• Then click!

That’s a lot of interaction, and fireEvent.click() only simulates one event.

So let’s go a step further.

Enter @testing-library/user-event

This library simulates real user behavior more accurately.

import userEvent from '@testing-library/user-event'

test('increments the counter', async () => {
  render(<Counter />)

  const button = screen.getByRole('button', { name: '0' })
  await userEvent.click(button)

  expect(button).toHaveTextContent('1')
})

Benefits of userEvent

• 🎯 Simulates real interaction flow
• 🎮 Fires all relevant events in the right order
• 🤝 Encourages user-first testing patterns

🧪 Explore how it works behind the scenes: click() source code

🧼 Recap: Avoid Implementation Details

🧠 Final Thoughts

Tests are only valuable if they continue to give you confidence after a refactor.

That means writing tests that focus on what the user sees and does, not how your component is built.

So next time you write a test, ask yourself:

“Would this still pass if I changed the HTML structure but kept the same behavior?”

If not, it’s time to ditch the implementation details.

📋 Practice + Reflect

Ready to practice this skill and retain what you learned? Fill out the elaboration and feedback form:

👉 Avoid Implementation Details – Feedback Form