Hide or show inline Common Lisp tests written with the testiere testing library. M-x testiere-toggle command that collapses or reveals the #+testiere sections.

This is how the code looks with testiere:

(defun add3 (x y z)
  "Adds three numbers"
  #+testiere
  (:tests
   (= 6 (add3 1 2 3))
   (:fails (add3 "hey"))
   (:fails (add3 1 2)))
  (+ x y z))

and this is how it looks toggled via M-x testiere-toggle:

(defun add3 (x y z)
  "Adds three numbers"
  #+testiere ...
  (+ x y z))

• Works from anywhere inside a supported def* form (defun, defmethod, deftype, defclass, defstruct) or from the header line itself

(use-package testiere-mode
  :vc (:fetcher github :repo "dotemacs/testiere-mode.el"))

1. Open a Common Lisp buffer that contains inline tests wrapped in a #+testiere block.
2. Place point either on the header line or anywhere inside the surrounding defun, defmethod, deftype, defclass, or defstruct form.
3. Run M-x testiere-toggle (or invoke the testiere-toggle-tests alias). The block will collapse into a friendly comment-like overlay.
4. Call the command again to reveal the tests. Repeated invocations cycle between the hidden and visible states.

Attach the command to a convenient key in the Lisp modes you use most:

(with-eval-after-load 'lisp-mode
  (define-key lisp-mode-map (kbd "C-c t") #'testiere-toggle))

(with-eval-after-load 'slime
  (define-key slime-mode-map (kbd "C-c t") #'testiere-toggle))

(with-eval-after-load 'sly
  (define-key sly-mode-map (kbd "C-c t") #'testiere-toggle))