3 files changed, 109 insertions, 6 deletions
diff --git a/tests/test-calendar-sync--expand-daily.el b/tests/test-calendar-sync--expand-daily.el
index 43b93664..0db9f345 100644
--- a/tests/test-calendar-sync--expand-daily.el
+++ b/tests/test-calendar-sync--expand-daily.el
@@ -176,5 +176,52 @@
          (occurrences (calendar-sync--expand-daily base-event rrule range)))
     (should (= (length occurrences) 5))))
 
+;;; UNTIL is inclusive (RFC 5545 3.3.10)
+
+(ert-deftest test-calendar-sync--expand-daily-until-includes-the-until-date ()
+  "Boundary: an occurrence falling ON the UNTIL date is kept.
+RFC 5545 3.3.10: UNTIL bounds the recurrence \"in an inclusive manner\", and
+when it lines up with the recurrence that date \"becomes the last instance\".
+A strict before-comparison drops it, so the last meeting of every bounded
+series silently vanishes from the agenda."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (until-date (test-calendar-sync-time-date-only 5))
+         (base-event (list :summary "Bounded Standup" :start start-date))
+         (rrule (list :freq 'daily :interval 1 :until until-date))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-daily base-event rrule range))
+         (last-start (plist-get (car (last occurrences)) :start)))
+    ;; day+1 through day+5 inclusive = 5 occurrences.
+    (should (= (length occurrences) 5))
+    ;; The final occurrence is the UNTIL date itself.
+    (should (equal (seq-take last-start 3) until-date))))
+
+(ert-deftest test-calendar-sync--expand-daily-until-excludes-dates-after-it ()
+  "Boundary: inclusivity stops at UNTIL; the next day is not generated.
+Guards the fix against over-correcting into an off-by-one the other way."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (until-date (test-calendar-sync-time-date-only 5))
+         (day-after (test-calendar-sync-time-date-only 6))
+         (base-event (list :summary "Bounded Standup" :start start-date))
+         (rrule (list :freq 'daily :interval 1 :until until-date))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-daily base-event rrule range))
+         (dates (mapcar (lambda (o) (seq-take (plist-get o :start) 3)) occurrences)))
+    (should (member until-date dates))
+    (should-not (member day-after dates))))
+
+(ert-deftest test-calendar-sync--expand-daily-until-on-start-date-yields-one ()
+  "Boundary: UNTIL equal to the start date yields exactly that one occurrence.
+The degenerate single-instance series -- a strict comparison returns nothing
+at all here, which is the same defect at its smallest."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (until-date (test-calendar-sync-time-date-only 1))
+         (base-event (list :summary "One Shot" :start start-date))
+         (rrule (list :freq 'daily :interval 1 :until until-date))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-daily base-event rrule range)))
+    (should (= (length occurrences) 1))
+    (should (equal (seq-take (plist-get (car occurrences) :start) 3) until-date))))
+
 (provide 'test-calendar-sync--expand-daily)
 ;;; test-calendar-sync--expand-daily.el ends here
diff --git a/tests/test-calendar-sync--expand-weekly.el b/tests/test-calendar-sync--expand-weekly.el
index a6143bce..0639ca07 100644
--- a/tests/test-calendar-sync--expand-weekly.el
+++ b/tests/test-calendar-sync--expand-weekly.el
@@ -270,5 +270,33 @@
         (should (= (length occurrences) 0)))
     (test-calendar-sync--expand-weekly-teardown)))
 
+;;; UNTIL is inclusive (RFC 5545 3.3.10)
+
+(ert-deftest test-calendar-sync--expand-weekly-until-includes-the-until-date ()
+  "Boundary: a weekly occurrence landing ON the UNTIL date is kept.
+The weekly loop checks UNTIL in two places -- the outer week-stepping guard
+and the per-weekday check inside it -- so it needs its own guard rather than
+inheriting the daily one.  Fixing the loop without this test left weekly
+silently unprotected: reverting the fix failed three daily tests and zero
+weekly ones."
+  (test-calendar-sync--expand-weekly-setup)
+  (unwind-protect
+      ;; Omitting :byday makes the series recur on the start date's own weekday,
+      ;; which anchors UNTIL exactly on an occurrence without hardcoding a date.
+      (let* ((start-date (test-calendar-sync-time-days-from-now 1 9 0))
+             (week-2 (test-calendar-sync-time-date-only 8))
+             (until-date (test-calendar-sync-time-date-only 15))
+             (week-4 (test-calendar-sync-time-date-only 22))
+             (base-event (list :summary "Bounded Weekly" :start start-date))
+             (rrule (list :freq 'weekly :interval 1 :until until-date))
+             (range (test-calendar-sync-wide-range))
+             (occurrences (calendar-sync--expand-weekly base-event rrule range))
+             (dates (mapcar (lambda (o) (seq-take (plist-get o :start) 3)) occurrences)))
+        ;; day+1, +8, +15 are consecutive same-weekday dates; UNTIL is the third.
+        (should (equal dates (list (seq-take start-date 3) week-2 until-date)))
+        ;; Inclusivity stops at UNTIL -- the following week is not generated.
+        (should-not (member week-4 dates)))
+    (test-calendar-sync--expand-weekly-teardown)))
+
 (provide 'test-calendar-sync--expand-weekly)
 ;;; test-calendar-sync--expand-weekly.el ends here
diff --git a/tests/test-calendar-sync-properties.el b/tests/test-calendar-sync-properties.el
index c25bb99f..0b01cbd9 100644
--- a/tests/test-calendar-sync-properties.el
+++ b/tests/test-calendar-sync-properties.el
@@ -77,12 +77,21 @@ For any COUNT value N, expansion never produces more than N occurrences."
 
 ;;; Property 2: UNTIL Boundary
 
+;; These two asserted the wrong invariant until 2026-07-16: they required every
+;; occurrence to fall strictly BEFORE UNTIL, which is the exclusive reading RFC
+;; 5545 3.3.10 contradicts ("bounds the recurrence rule in an inclusive manner";
+;; a UNTIL synchronized with the recurrence "becomes the last instance").  They
+;; were written against the expansion loop's strict `before-date-p' guard and so
+;; pinned the very defect that dropped the last instance of every bounded series.
+;; The property is on-or-before; the upper bound is what UNTIL is for.
+
 (ert-deftest test-calendar-sync-property-until-bounds-daily ()
-  "Property: No daily occurrence starts on or after UNTIL date."
+  "Property: no daily occurrence starts after the UNTIL date.
+UNTIL is an inclusive bound (RFC 5545 3.3.10), so landing exactly on it is
+correct and only a later date violates the property."
   (dotimes (_ test-calendar-sync-property-trials)
     (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
            (until-days (+ 10 (random 60)))
-           ;; UNTIL must be date-only (3 elements) for calendar-sync--before-date-p
            (until-date (test-calendar-sync-time-date-only until-days))
            (base-event (list :summary "Until Test" :start start-date))
            (rrule (list :freq 'daily :interval 1 :until until-date))
@@ -90,16 +99,35 @@ For any COUNT value N, expansion never produces more than N occurrences."
            (occurrences (calendar-sync--expand-daily base-event rrule range)))
       (dolist (occ occurrences)
         (let ((occ-start (plist-get occ :start)))
-          (should (calendar-sync--before-date-p
+          (should (calendar-sync--date-on-or-before-p
                    (list (nth 0 occ-start) (nth 1 occ-start) (nth 2 occ-start))
                    until-date)))))))
 
+(ert-deftest test-calendar-sync-property-until-bounds-daily-reaches-until ()
+  "Property: a daily series stepping by one day always reaches its UNTIL date.
+With interval 1 the recurrence is synchronized with any UNTIL, so the last
+instance must be UNTIL itself.  This is the half the old exclusive property
+could never have caught -- it only bounded from above, so silently dropping
+the final occurrence satisfied it."
+  (dotimes (_ test-calendar-sync-property-trials)
+    (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+           (until-days (+ 10 (random 60)))
+           (until-date (test-calendar-sync-time-date-only until-days))
+           (base-event (list :summary "Until Test" :start start-date))
+           (rrule (list :freq 'daily :interval 1 :until until-date))
+           (range (test-calendar-sync-wide-range))
+           (occurrences (calendar-sync--expand-daily base-event rrule range))
+           (last-start (plist-get (car (last occurrences)) :start)))
+      (should occurrences)
+      (should (equal (seq-take last-start 3) until-date)))))
+
 (ert-deftest test-calendar-sync-property-until-bounds-weekly ()
-  "Property: No weekly occurrence starts on or after UNTIL date."
+  "Property: no weekly occurrence starts after the UNTIL date.
+UNTIL is an inclusive bound (RFC 5545 3.3.10), so landing exactly on it is
+correct and only a later date violates the property."
   (dotimes (_ test-calendar-sync-property-trials)
     (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
            (until-days (+ 14 (random 60)))
-           ;; UNTIL must be date-only (3 elements) for calendar-sync--before-date-p
            (until-date (test-calendar-sync-time-date-only until-days))
            (weekdays (test-calendar-sync-random-weekday-subset))
            (base-event (list :summary "Until Test" :start start-date))
@@ -108,7 +136,7 @@ For any COUNT value N, expansion never produces more than N occurrences."
            (occurrences (calendar-sync--expand-weekly base-event rrule range)))
       (dolist (occ occurrences)
         (let ((occ-start (plist-get occ :start)))
-          (should (calendar-sync--before-date-p
+          (should (calendar-sync--date-on-or-before-p
                    (list (nth 0 occ-start) (nth 1 occ-start) (nth 2 occ-start))
                    until-date)))))))