@sinonjs/samsam is a small, versatile assertion library, part of the Sinon.JS ecosystem. It rigorously compares values for equality and deep equality, going beyond basic JavaScript comparisons. Samsam includes matchers for checking type, properties, and even regular expression matches. This library is invaluable for writing robust unit tests that require precise and reliable value verification. It is essential for building reliable test suites around Sinon.JS mocking and stubbing framework.