1. Jest: Jest is a popular JavaScript testing framework that focuses on simplicity and ease of use. It is often used for testing React applications but can also be used for testing any JavaScript code. One key difference with Jest is its built-in assertion library, which allows you to write tests without the need for additional assertion libraries.
2. Nightwatchjs: Nightwatchjs, on the other hand, is an end-to-end testing framework that is primarily used for testing web applications. It provides a simple and intuitive API for interacting with web elements, making it easy to write tests for various browser actions. One key difference with Nightwatchjs is its support for multiple browsers, allowing you to run tests on different browsers simultaneously.
3. Jest: Jest provides features like automatic mocking, snapshot testing, and code coverage reporting out of the box. This makes it easier to write and maintain tests, as well as to identify areas of your codebase that are not fully covered by your tests. Nightwatchjs does not have these built-in features and requires additional setup and plugins to achieve similar functionalities.
4. Nightwatchjs: Nightwatchjs supports parallel test execution, which can significantly reduce the time required to run a large test suite. This is particularly useful for organizations with a fast-paced development cycle or large codebases. Jest does not have native support for parallel test execution and requires external tools or configurations to achieve similar performance improvements.
5. Jest: Jest has a vibrant community and a wide range of plugins and extensions available. This allows you to easily extend and customize Jest to fit your testing needs. Nightwatchjs, while also having a community and plugin ecosystem, is generally less popular and may have fewer resources available for specific use cases or integrations.
6. Nightwatchjs: Nightwatchjs provides extensive browser automation capabilities, including support for Selenium WebDriver. This allows you to test complex browser interactions, such as form submission, AJAX requests, and browser navigation. Jest, although it has basic browser capability through jsdom, does not have the same level of browser automation features as Nightwatchjs.

In summary, Jest is a JavaScript testing framework that focuses on simplicity and ease of use, with built-in assertion library and advanced testing features, while Nightwatchjs is an end-to-end testing framework primarily used for web applications, with support for multiple browsers, parallel test execution, and extensive browser automation capabilities.