Check for presuppositions in `calendar-date-is-valid-p'

Do not signal an error in `calendar-date-is-valid-p' if passed a
value which is not a three-element list of integers.  Signaling
an error makes the function unusable as a predicate for valid
date values. (Bug#74848)
* lisp/calendar/calendar.el (calendar-date-is-valid-p): Add the
check that input is a 3-element list.
* test/lisp/calendar/calendar-tests.el: New file with tests.

1 files changed, 34 insertions, 0 deletions

diff --git a/test/lisp/calendar/calendar-tests.el b/test/lisp/calendar/calendar-tests.el
new file mode 100644
index 00000000000..c41f14d3b54
--- /dev/null
+++ b/test/lisp/calendar/calendar-tests.el
@@ -0,0 +1,34 @@
+;;; calendar-tests.el --- tests for calendar/calendar.el  -*- lexical-binding:t -*-
+
+;; Copyright (C) 2024 Free Software Foundation, Inc.
+
+;; Author: Richard Lawrence <rwl@recursewithless.net>
+
+;; 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/>.
+
+;;; Code:
+
+(require 'ert)
+(require 'calendar)
+
+(ert-deftest calendar-test-validity-predicate ()
+  (should (eq (calendar-date-is-valid-p nil) nil))
+  (should (eq (calendar-date-is-valid-p "invalid") nil))
+  (should (eq (calendar-date-is-valid-p (list 1 2)) nil))
+  (should (eq (calendar-date-is-valid-p (list 5 1 2025)) t)))
+
+(provide 'calendar-tests)
+;;; calendar-tests.el ends here