This repository is the `@testing-library/jest-dom` library, a widely-used collection of custom Jest matchers for asserting the state of DOM elements in tests. It provides over 30 matchers such as `toBeVisible`, `toBeDisabled`, `toHaveAttribute`, `toHaveFormValues`, and `toHaveAccessibleName`, enabling declarative and readable test assertions. The library is designed to work with Jest, Vitest, Bun, and any Jest-compatible `expect` interface, with dedicated entry points for each. It leverages dependencies like `aria-query` and `dom-accessibility-api` to support accessibility-related matchers, and `@adobe/css-tools` for CSS style assertions. The codebase is well-structured, with each matcher in its own file, a shared utility module, and a factory pattern for generating query-based matchers (`toContainAnyBy*` / `toContainOneBy*`). Comprehensive tests and TypeScript type definitions are included. The library is actively maintained with frequent releases and a large contributor base.