(assert x) (assert x message)
Evaluates expr and throws an exception if it does not evaluate to logical true.
user=> (assert true)
nil
user=> (assert false)
java.lang.AssertionError: Assert failed: false (NO_SOURCE_FILE:0)
user=> (assert nil)
java.lang.AssertionError: Assert failed: nil (NO_SOURCE_FILE:0)
user=> (assert 0)
nil
user=> (assert [1 2 3])
nil
user=> (assert "foo")
nil
;; Messages can help you track down what went wrong.
user=> (assert (= 5 (+ 2 2)) "There are four lights!")
AssertionError Assert failed: There are four lights!