Fix misspelled functions in shortdoc groups

* lisp/emacs-lisp/shortdoc.el (file, list): Fix misspelled function
names: 'file-writable-p' and 'seq-reduce'.
* test/lisp/emacs-lisp/shortdoc-tests.el (subr-x): Require.
(shortdoc-all-functions-fboundp): New test.

lisp/emacs-lisp/shortdoc.el

@@ -421,8 +421,8 @@ A FUNC form can have any number of `:no-eval' (or `:no-value'),
   (file-readable-p
    :no-eval (file-readable-p "/tmp/foo")
    :eg-result t)
-  (file-writeable-p
-   :no-eval (file-writeable-p "/tmp/foo")
+  (file-writable-p
+   :no-eval (file-writable-p "/tmp/foo")
    :eg-result t)
   (file-accessible-directory-p
    :no-eval (file-accessible-directory-p "/tmp")
@@ -652,8 +652,8 @@ A FUNC form can have any number of `:no-eval' (or `:no-value'),
    :eval (mapcan #'list '(1 2 3)))
   (mapc
    :eval (mapc #'insert '("1" "2" "3")))
-  (reduce
-   :eval (reduce #'+ '(1 2 3)))
+  (seq-reduce
+   :eval (seq-reduce #'+ '(1 2 3) 0))
   (mapconcat
    :eval (mapconcat #'identity '("foo" "bar") "|"))
   "Predicates"

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

@@ -21,6 +21,7 @@
 
 (require 'ert)
 (require 'shortdoc)
+(require 'subr-x) ; `string-pad' in shortdoc group needed at run time
 
 (defun shortdoc-tests--tree-contains (tree fun)
   "Whether TREE contains a call to FUN."
@@ -44,6 +45,14 @@
                 (should (shortdoc-tests--tree-contains expr fun))))
             (setq props (cddr props))))))))
 
+(ert-deftest shortdoc-all-functions-fboundp ()
+  "Check that all functions listed in shortdoc groups are `fboundp'."
+  (dolist (group shortdoc--groups)
+    (dolist (item group)
+      (when (consp item)
+        (let ((fun (car item)))
+          (should (fboundp fun)))))))
+
 (ert-deftest shortdoc-all-groups-work ()
   "Test that all defined shortdoc groups display correctly."
   (dolist (group (mapcar (lambda (x) (car x)) shortdoc--groups))