is

(is form) (is form msg)

Asserts form and answers its value. A truthy value passes; anything else reports FAIL in (test) (file:line), the testing contexts, msg, the expected form and the actual value. For a function call the arguments are evaluated first and the actual value is (not (f values...)); for a macro, a special form, a local or a keyword it is the value itself. An error inside form reports ERROR and answers nil. (thrown? C body...) passes when the body throws an exception a catch of C takes and answers it; (thrown-with-msg? C re body...) also requires re to find a match in the message. An exception of another class reports ERROR, like the oracle's. Outside run-tests the report still prints, without counting.

true

FAIL in () (NO_SOURCE_FILE:3)
strings differ
expected: (= "a" "b")
  actual: (not (= "a" "b"))
false
clojure.lang.ExceptionInfo: boom {}