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Assertion

Assertions to validate method input/output with nice error messages.

Power Assert in JavaScript. Provides descriptive assertion messages through standard assert interface. No API is the best API.

AssertJ is a library providing easy to use rich typed assertions 

Minimalistic BDD-style assertions for Node.JS and the browser.

Should testing for .NET - the way Asserting *Should* be!

Extends Chai with assertions for the Sinon.JS mocking framework.