(require 'ert)

(defvar ivy-expr nil
  "Holds a test expression to evaluate with `ivy-eval'.")

(defvar ivy-result nil
  "Holds the eval result of `ivy-expr' by `ivy-eval'.")

(defun ivy-eval ()
  "Evaluate `ivy-expr'."
  (interactive)
  (setq ivy-result (eval ivy-expr)))

(global-set-key (kbd "C-c e") 'ivy-eval)

(defun ivy-with (expr keys)
  "Evaluate EXPR followed by KEYS."
  (let ((ivy-expr expr))
    (execute-kbd-macro
     (vconcat (kbd "C-c e")
              (kbd keys)))
    ivy-result))

(ert-deftest ivy-read ()
  (should (equal
           (ivy-read "pattern: " nil)
           nil))
  (should (equal
           (ivy-read "pattern: " '("42"))
           "42"))
  (should (equal
           (ivy-with '(ivy-read "pattern: " '("blue" "yellow"))
                     "C-m")
           "blue"))
  (should (equal
           (ivy-with '(ivy-read "pattern: " '("blue" "yellow"))
                     "y C-m")
           "yellow"))
  (should (equal
           (ivy-with '(ivy-read "pattern: " '("blue" "yellow"))
                     "y DEL b C-m")
           "blue"))
  (should (equal
           (ivy-with '(ivy-read "pattern: " '("blue" "yellow"))
                     "z C-m")
           nil)))