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+;;; test-chime-days-until-event.el --- Tests for chime--days-until-event -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2024-2026 Craig Jennings
+
+;; Author: Craig Jennings <c@cjennings.net>
+
+;; This program 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.
+
+;; This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Unit tests for `chime--days-until-event' and the notification text that
+;; consumes it.
+;;
+;; The function maps over every timestamp on an event and keeps the day
+;; count for the all-day ones.  Timed timestamps map to nil, so an event
+;; mixing a timed and an all-day timestamp used to hand `-min' a list with
+;; a nil in it and signal wrong-type-argument.  An event with no all-day
+;; timestamp at all handed `-min' an empty list, which signals too.  Both
+;; crash on every tick once `chime-day-wide-advance-notice' is on, walking
+;; the async failure counter up to the persistent-failure warning.
+;;
+;; Tests cover normal cases, boundary cases, and error cases.
+
+;;; Code:
+
+(require 'test-bootstrap (expand-file-name "test-bootstrap.el"))
+
+;;; Helpers
+
+;; `chime--days-until-event' measures against `current-time', so these
+;; timestamps hang off the real now.  testutil-time's `test-time-now' is
+;; deliberately 30 days ahead, which would make every expected day count
+;; wrong here.
+
+(defun test-chime-days--offset-time (days-from-now)
+  "Return the time DAYS-FROM-NOW days from the real current time."
+  (time-add (current-time) (days-to-time days-from-now)))
+
+(defun test-chime-days--all-day (days-from-now)
+  "Return an all-day timestamp cons cell DAYS-FROM-NOW days out."
+  (let ((ts (test-timestamp-string (test-chime-days--offset-time days-from-now) t)))
+    (cons ts (chime--timestamp-parse ts))))
+
+(defun test-chime-days--timed (days-from-now hour minute)
+  "Return a timed timestamp cons cell DAYS-FROM-NOW days out at HOUR:MINUTE."
+  (let* ((decoded (decode-time (test-chime-days--offset-time days-from-now)))
+         (time (encode-time 0 minute hour
+                            (decoded-time-day decoded)
+                            (decoded-time-month decoded)
+                            (decoded-time-year decoded)))
+         (ts (test-timestamp-string time)))
+    (cons ts (chime--timestamp-parse ts))))
+
+;;; Normal Cases
+
+(ert-deftest test-chime-days-until-event-single-all-day-timestamp ()
+  "A lone all-day timestamp yields its day count."
+  (should (= (chime--days-until-event (list (test-chime-days--all-day 3))) 3)))
+
+(ert-deftest test-chime-days-until-event-returns-the-soonest ()
+  "The soonest all-day timestamp wins."
+  (should (= (chime--days-until-event
+              (list (test-chime-days--all-day 5)
+                    (test-chime-days--all-day 2)
+                    (test-chime-days--all-day 9)))
+             2)))
+
+;;; Boundary Cases
+
+(ert-deftest test-chime-days-until-event-mixed-timed-and-all-day ()
+  "An event mixing a timed and an all-day timestamp ignores the timed one.
+The timed timestamp maps to nil, which must not reach `-min'."
+  (should (= (chime--days-until-event
+              (list (test-chime-days--timed 8 14 0)
+                    (test-chime-days--all-day 4)))
+             4)))
+
+(ert-deftest test-chime-days-until-event-timed-only-returns-nil ()
+  "With no all-day timestamp there is no day count, so the result is nil."
+  (should-not (chime--days-until-event
+               (list (test-chime-days--timed 2 9 30)
+                     (test-chime-days--timed 6 17 0)))))
+
+(ert-deftest test-chime-days-until-event-empty-list-returns-nil ()
+  "An event with no timestamps at all yields nil rather than signalling."
+  (should-not (chime--days-until-event '())))
+
+;;; Error Cases
+
+(ert-deftest test-chime-days-until-event-mixed-timestamps-do-not-signal ()
+  "The mixed-timestamp case must not signal wrong-type-argument.
+This is the crash that recurred every tick and drove the async failure
+counter to the persistent-failure warning."
+  (should-not (condition-case nil
+                  (progn (chime--days-until-event
+                          (list (test-chime-days--timed 8 14 0)
+                                (test-chime-days--all-day 4)))
+                         nil)
+                (error t))))
+
+(ert-deftest test-chime-day-wide-notification-text-survives-nil-day-count ()
+  "The notification text falls back rather than crashing on a nil day count.
+`chime--days-until-event' returns nil when an event has no all-day
+timestamp, so the advance-notice branch must not compare nil to a number."
+  (let ((chime-day-wide-advance-notice 7)
+        (event `((title . "Timed Only")
+                 (times . (,(test-chime-days--timed 3 10 0)))
+                 (intervals . ((0)))
+                 (marker-file . "/tmp/test.org")
+                 (marker-pos . 1))))
+    (cl-letf (((symbol-function 'chime--event-has-any-passed-time)
+               (lambda (_event) nil))
+              ((symbol-function 'chime--event-within-advance-notice-window)
+               (lambda (_event) t)))
+      (let ((text (chime--day-wide-notification-text event)))
+        (should (stringp text))
+        (should (string-match-p "Timed Only" text))))))
+
+(provide 'test-chime-days-until-event)
+;;; test-chime-days-until-event.el ends here