Sinon-Chai: Sinon.JS Assertions for Chai

Sinon-Chai is a testing utility that integrates the Sinon.JS mocking framework with the Chai assertion library, allowing developers to write more expressive and readable assertions for spies, stubs, and mocks. Instead of using Sinon's direct assertion methods (`sinon.assert.calledWith`) or awkward Chai property checks, Sinon-Chai extends Chai's `should` and `expect` interfaces to provide natural language assertions like `expect(mySpy).to.have.been.calledWith('foo')`. The current stable version is 4.0.1, which supports Chai v5 and v6, and Sinon v4+. The library maintains an active release cadence, typically updating to support new major versions of its peer dependencies, Chai and Sinon. Key differentiators include its seamless integration into the Chai assertion chain, improving test readability and developer experience by providing a unified assertion style across a test suite. It's widely used in JavaScript testing environments for both Node.js and browser applications.