Adding your own spec for filter

filter_spec.clj

(require '[clojure.spec.test.alpha :as st])
(require '[clojure.spec.alpha :as s])
(require '[expound.alpha :as expound])

(set! s/*explain-out* expound/printer)

(st/instrument)
(filter 123 "12333333333333") ; java.lang.Long cannot be cast to clojure.lang.IFn

(s/fdef clojure.core/filter
        :args (s/cat :pred ifn? :coll (s/? coll?)))

(st/instrument)

(filter 123 "12333333333333")

;; ExceptionInfo Call to #'clojure.core/filter did not conform to spec:
;; form-init3643830678794618507.clj:1

;; -- Spec failed --------------------

;; Function arguments

;; (123 ...)
;; ^^^

;; should satisfy

;; ifn?



;; -------------------------
;; Detected 1 error