Regex Tester & Validator

Matches unexpected.js-style test assertions such as `expect(el, "to contain elements matching", "[data-test-id=foo]")`, capturing the asserted subject name and the data-test-id value (word chars and hyphens). Typically used in codemods, linters, or migration scripts that parse and rewrite frontend test code, e.g., extracting data-test-id selectors from DOM-based assertions.