Trying to write a failing test with check-var

game_test.clj

(ns blackjack.game-test
  (:require [clojure.spec :as s]
            [clojure.spec.test :as test]))

(def suits #{:hearts :diamonds :clubs :spades})

(def ranks (into #{:ace :king :queen :jack} (range 2 11)))

(def cards (for [rank ranks suit suits] [rank suit]))

(s/def ::card (s/cat :rank ranks :suit suits))

(defn value [[rank _]]
  (cond
    (<= 2 rank 10)
    rank

    (#{:jack :queen :king} rank)
    10

    (#{:ace} rank)
    [1 11]))

(s/fdef value
        :args (s/cat :card ::card)
        :ret  integer?)

(s/instrument-all)

(test/check-var #'value)
;; => nil