Jest is an open-source JavaScript testing framework developed by Facebook, with a main focus on simplicity. It is a significant part of the Tech Skills category as it is used by many companies to test JavaScript code, thereby ensuring code reliability and top quality applications. As a result of the critical role it plays in the software development process, the ability to skillfully use Jest is highly sought after in the job market, and it's a key competency for roles such as software developers, test engineers, and quality assurance professionals.

Recruiters looking for expertise in Jest are seeking candidates who can write and maintain comprehensive test suites for applications. These individuals can leverage features that Jest offers, like a zero-configuration testing experience, support for Babel, TypeScript, Node, React, Angular, Vue and others, snapshot testing, async function testing, and parallel test execution.

Apart from the ability to write tests, understanding the principles behind test-driven development (TDD) and having a good grasp of JavaScript, the language Jest tests are written in, are also vital. Experience with version control systems like Git and collaboration tools like GitHub is beneficial, as these are typically used in real-world software development environments.

Gaining prowess in Jest might be more accessible for those who have a strong foundation in JavaScript principals. Understanding the basics of testing theories like unit testing, integration testing, and functional testing will also be of great help. Familiarity with other JavaScript testing frameworks such as Mocha or Jasmine can provide a smoother transition to Jest, given their similar concepts and functionality. Lastly, a background in development frameworks that Jest supports, such as React or Vue.js, could be very beneficial as it enables creating more targeted and effective tests.