`is` is a `clojure.test` macro for evaluating an assertion expression and reporting a readable result. It verifies truthiness, accepts an optional descriptive message, and exposes expected and actual values when an assertion fails. section 22.9
Readable assertion failure
```clojure (deftest sqrt-test (is (= 2 (sqrt 4)) "Expecting 2")) ``` A failing test reports the message, expected expression, and actual value—for example, a computed `2.000000000000002` instead of exact `2`. section 22.9
