How do you use styles in React Native?

Testing React Native components can be accomplished using libraries like Jest for unit and snapshot testing, and React Testing Library for rendering components and asserting their behavior. Jest provides a framework for writing and running tests, while React Testing Library helps ensure that components render and behave correctly by focusing on user interactions.

`react-native-fs` is a library that allows you to interact with the file system in React Native applications. It provides methods for reading, writing, and deleting files on the device's storage. This is useful for tasks like storing user data, caching files, and accessing files from different directories. It supports both iOS and Android platforms.

App state in React Native can be managed using various methods. For simpler state management, you can use the Context API or React's `useState` and `useReducer` hooks. For more complex state needs, libraries like Redux or MobX offer advanced state management solutions. These libraries help you manage state across your application and keep it in sync with the UI.

`useReducer` is a hook used in React Native to manage complex state logic in functional components. It works similarly to Redux's reducer, allowing you to manage state transitions through actions. It is useful for managing state that involves multiple sub-values or when the next state depends on the previous one. It provides better performance and clarity for complex state interactions.