Add tests for rot13.el

* lisp/rot13.el (rot13): Docstring correction.

* test/lisp/rot13-tests.el: New file with tests for rot13.el.

lisp/rot13.el

@@ -63,7 +63,10 @@
 
 ;;;###autoload
 (defun rot13 (object &optional start end)
-  "Return ROT13 encryption of OBJECT, a buffer or string."
+  "ROT13 encrypt OBJECT, a buffer or string.
+If OBJECT is a buffer, encrypt the region between START and END.
+If OBJECT is a string, encrypt it in its entirety, ignoring START
+and END, and return the encrypted string."
   (if (bufferp object)
       (with-current-buffer object
 	(rot13-region start end))

test/lisp/rot13-tests.el

+;;; rot13-tests.el --- Tests for rot13.el  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2016 Free Software Foundation, Inc.
+
+;; Author: Simen Heggestøyl <simenheg@gmail.com>
+;; Keywords:
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+
+;;; Code:
+
+(require 'ert)
+(require 'rot13)
+
+(ert-deftest rot13-tests-rot13 ()
+  (should (equal (rot13 "Super-secret text") "Fhcre-frperg grkg"))
+  (with-temp-buffer
+    (insert "Super-secret text")
+    (rot13 (current-buffer) (point-min) (point-max))
+    (should (equal (buffer-string) "Fhcre-frperg grkg"))
+    (rot13 (current-buffer) (point-min) (+ (point-min) 5))
+    (should (equal (buffer-string) "Super-frperg grkg"))))
+
+(ert-deftest rot13-tests-rot13-string ()
+  (should (equal (rot13-string "") ""))
+  (should (equal (rot13-string (rot13-string "foo")) "foo"))
+  (should (equal (rot13-string "Super-secret text")
+                 "Fhcre-frperg grkg")))
+
+(ert-deftest rot13-tests-rot13-region ()
+  (with-temp-buffer
+    (insert "Super-secret text")
+    (rot13-region (+ (point-min) 6) (+ (point-min) 12))
+    (should (equal (buffer-string) "Super-frperg text"))))
+
+(provide 'rot13-tests)
+;;; rot13-tests.el ends here