Component Testing

Problem

Components break in subtle ways that only appear in production. Developers manually click through the UI repeatedly to verify changes, wasting hours on repetitive testing. Regression bugs slip through because there’s no automated verification that components render correctly or handle user interactions properly.

Solution

Write tests that render components, simulate user interactions, and assert on output to verify behavior in isolation. This catches regressions early and ensures components work correctly before integrating them into larger systems.

Example

This example demonstrates how to render a component in isolation, simulate user interaction, and verify the expected behavior is triggered.

import { render, fireEvent } from '@testing-library/react';

test('button calls onClick when clicked', () => {
  // Create a mock function to track if onClick is called
  const handleClick = jest.fn();

  // Render the Button component in isolation with test props
  const { getByText } = render(<Button onClick={handleClick}>Click</Button>);

  // Simulate a user clicking the button
  fireEvent.click(getByText('Click'));

  // Assert the onClick handler was called exactly once
  expect(handleClick).toHaveBeenCalledTimes(1);
});

Benefits

• Catches component regressions before they reach production.
• Provides fast feedback during development without manual testing.
• Documents expected component behavior through test cases.
• Enables confident refactoring with automated regression detection.
• Reduces time spent on repetitive manual QA testing.

Tradeoffs

• Requires time and effort to write and maintain tests.
• Tests can become brittle if they rely on implementation details.
• May give false confidence if tests don’t cover real-world scenarios.
• Needs mocking for external dependencies which adds complexity.
• Can slow down development if test suite becomes too large or slow.