Hello.

In my last patch, I found a duplicate test, so I decided to find all of
the duplicate tests inside testing/lisp/ folder via this function:

(defun count-duplicate-tests (&optional directory)
  (let (files)
    (dolist (file (directory-files (or directory default-directory) t (rx ".el" string-end) t))
      (with-current-buffer (find-file-noselect file)
	(save-excursion
          (goto-char (point-min))
          (while (search-forward "(ert-deftest" nil t)
	    (ignore-errors
	      (while-let((form (or (read (current-buffer)) t)))
		(when (eq (car-safe form) 'should)
		  (setf
		   (alist-get form (alist-get file files nil nil #'equal) 0 nil #'equal)
		   (1+ (alist-get form (alist-get file files nil nil #'equal) 0 nil #'equal))))))))))
    (seq-remove
     (lambda(file) (null (cdr file)))
     (mapcar
      (lambda(file)
	(cons
	 (car file)
	 (seq-filter
	  (lambda(form) (/= (cdr form) 1))
	  (cdr file))))
      files))))

(setq dups (count-duplicate-tests "~/org-mode/testing/lisp/"))

Then I checked the result manually and deleted some of them.

Here is the patch I wrote: