tn.clj

(defn true-or-nil? [x]
  (or (true? x) (nil? x)))

;; this test passes
(expect (interaction (spit #"/tmp/" String :append true-or-nil?))
        (do
          (spit "/tmp/somewhere-else" "nil")
          (spit "/tmp/hello-world" "some data" :append true)))

;; so does this test
(expect (interaction (spit #"/tmp/" String :append true-or-nil?))
        (do
          (spit "/tmp/somewhere-else" "nil")
          (spit "/tmp/hello-world" "some data" :append nil)))

;; this test fails
(expect (interaction (spit #"/tmp/" String :append true-or-nil?))
        (do
          (spit "/tmp/somewhere-else" "nil")
          (spit "/tmp/hello-world" "some data" :append "not true or nil")))