Fix shortdoc examples

Make sure that each example in shortdoc actually contains the function
it illustrates, and add a test for it.

* lisp/emacs-lisp/shortdoc.el (string, list, buffer, number):
Use the right functions in examples for string-version-lessp,
lax-plist-put, point-min and ffloor.
* test/lisp/emacs-lisp/shortdoc-tests.el: New test file.

lisp/emacs-lisp/shortdoc.el

@@ -221,7 +221,7 @@ There can be any number of :example/:result elements."
   (string-greaterp
    :eval (string-greaterp "foo" "bar"))
   (string-version-lessp
-   :eval (string-lessp "foo32.png" "bar4.png"))
+   :eval (string-version-lessp "pic4.png" "pic32.png"))
   (string-prefix-p
    :eval (string-prefix-p "foo" "foobar"))
   (string-suffix-p
@@ -613,7 +613,7 @@ There can be any number of :example/:result elements."
   (lax-plist-get
    :eval (lax-plist-get '("a" 1 "b" 2 "c" 3) "b"))
   (lax-plist-put
-   :no-eval (setq plist (plist-put plist "d" 4))
+   :no-eval (setq plist (lax-plist-put plist "d" 4))
    :eq-result '("a" 1 "b" 2 "c" 3 "d" 4))
   (plist-member
    :eval (plist-member '(a 1 b 2 c 3) 'b))
@@ -838,7 +838,7 @@ There can be any number of :example/:result elements."
   (point
    :eval (point))
   (point-min
-   :eval (point-max))
+   :eval (point-min))
   (point-max
    :eval (point-max))
   (line-beginning-position
@@ -1056,7 +1056,7 @@ There can be any number of :example/:result elements."
   (logb
    :eval (logb 10.5))
   (ffloor
-   :eval (floor 1.2))
+   :eval (ffloor 1.2))
   (fceiling
    :eval (fceiling 1.2))
   (ftruncate

test/lisp/emacs-lisp/shortdoc-tests.el

@@ -0,0 +1,45 @@
+;;; shortdoc-tests.el --- tests for shortdoc.el   -*- lexical-binding: t -*-
+
+;; Copyright (C) 2021 Free Software Foundation, Inc.
+
+;; 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 <https://www.gnu.org/licenses/>.
+
+(require 'ert)
+(require 'shortdoc)
+
+(defun shortdoc-tests--tree-contains (tree fun)
+  "Whether TREE contains a call to FUN."
+  (and (proper-list-p tree)
+       (or (eq (car tree) fun)
+           (cl-some (lambda (x) (shortdoc-tests--tree-contains x fun)) tree))))
+
+(ert-deftest shortdoc-examples ()
+  "Check that each example actually contains the corresponding form."
+  (dolist (group shortdoc--groups)
+    (dolist (item group)
+      (when (consp item)
+        (let ((fun (car item))
+              (props (cdr item)))
+          (while props
+            (when (memq (car props) '(:eval :no-eval :no-eval*))
+              (let* ((example (cadr props))
+                     (expr (cond
+                            ((consp example) example)
+                            ((stringp example) (read example)))))
+                (should (shortdoc-tests--tree-contains expr fun))))
+            (setq props (cddr props))))))))
+
+(provide 'shortdoc-tests)