Testing useRef in Jest with React Components

This challenge focuses on testing React components that utilize the useRef hook in Jest. useRef is crucial for accessing DOM elements or storing mutable values that persist across renders without causing re-renders. Effectively testing its usage ensures the component interacts correctly with its DOM or manages its internal state as expected.

Problem Description

You are tasked with writing Jest tests for a React component named CounterWithFocusButton. This component displays a count and has a button that, when clicked, focuses an input field. The useRef hook is used to obtain a reference to the input element for focusing.

What needs to be achieved:

Write Jest tests using @testing-library/react to verify the behavior of the CounterWithFocusButton component.

Key requirements:

1. Initial State: Verify that the component renders with the correct initial count and that the input field is not focused by default.
2. Button Click and Focus: When the "Focus Input" button is clicked, assert that the input field receives focus.
3. Counter Increment: When the "Increment" button is clicked, verify that the displayed count increases correctly.
4. DOM Reference Persistence: Although harder to directly "test" in this scenario, the tests should implicitly confirm that the ref is correctly attached and usable for DOM manipulation.

Expected behavior:

• On initial render, the count should be 0, and the input should not have focus.
• Clicking the "Focus Input" button should result in the input element having the document.activeElement set to it.
• Clicking the "Increment" button should update the displayed count by 1.

Edge cases to consider:

• What happens if the component is unmounted while trying to focus? (While not directly testable in this simplified example without mocking timers, be mindful of potential issues with direct DOM manipulation.) For this challenge, we will assume standard mounting and interaction.

Examples

Example 1: Initial Render

Input:
<CounterWithFocusButton />

Output (simulated DOM state):
- Count displayed: "0"
- Input element exists and does not have focus.

Example 2: Focusing the Input

Input:
<CounterWithFocusButton />

Actions:
1. Click the "Focus Input" button.

Output (simulated DOM state):
- Input element now has focus (document.activeElement points to it).

Example 3: Incrementing the Counter

Input:
<CounterWithFocusButton />

Actions:
1. Click the "Increment" button.
2. Click the "Increment" button again.

Output (simulated DOM state):
- Count displayed: "2"

Constraints

• The component must be written in TypeScript.
• The tests must be written in TypeScript using Jest and @testing-library/react.
• You should not directly mock useRef itself, but rather test its effect on the component's behavior.
• Focus on testing the observable behavior of the component.

Notes

• @testing-library/react provides utilities like render, screen, fireEvent, and waitFor that will be very useful.
• You can check for focus using document.activeElement.
• Remember to import necessary React and testing library modules.
• Consider the order of operations in your tests. Sometimes, waiting for an asynchronous update might be necessary, although for basic focus and state updates, it's often synchronous.