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+;;; test-calendar-sync--collect-exdates.el --- Tests for EXDATE collection  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Unit tests for calendar-sync--collect-exdates function.
+;; Tests collection of all excluded dates from an event, handling timezone conversion.
+;; Following quality-engineer.org guidelines: one function per file.
+
+;;; Code:
+
+(require 'ert)
+(add-to-list 'load-path (expand-file-name "." (file-name-directory load-file-name)))
+(add-to-list 'load-path (expand-file-name "../modules" (file-name-directory load-file-name)))
+(require 'testutil-calendar-sync)
+(require 'calendar-sync)
+
+;;; Normal Cases
+
+(ert-deftest test-calendar-sync--collect-exdates-normal-single-returns-list ()
+  "Test collecting single EXDATE returns list with one parsed value."
+  (let ((event "BEGIN:VEVENT
+DTSTART:20260203T130000
+RRULE:FREQ=WEEKLY;BYDAY=TU
+EXDATE:20260210T130000
+SUMMARY:Weekly Meeting
+END:VEVENT"))
+    (let ((result (calendar-sync--collect-exdates event)))
+      (should (listp result))
+      (should (= 1 (length result)))
+      (should (equal '(2026 2 10 13 0) (car result))))))
+
+(ert-deftest test-calendar-sync--collect-exdates-normal-multiple-returns-all ()
+  "Test collecting multiple EXDATEs returns all parsed values."
+  (let ((event "BEGIN:VEVENT
+DTSTART:20260203T130000
+RRULE:FREQ=WEEKLY;BYDAY=TU
+EXDATE:20260210T130000
+EXDATE:20260217T130000
+EXDATE:20260224T130000
+SUMMARY:Weekly Meeting
+END:VEVENT"))
+    (let ((result (calendar-sync--collect-exdates event)))
+      (should (= 3 (length result)))
+      (should (member '(2026 2 10 13 0) result))
+      (should (member '(2026 2 17 13 0) result))
+      (should (member '(2026 2 24 13 0) result)))))
+
+(ert-deftest test-calendar-sync--collect-exdates-normal-tzid-converts-to-local ()
+  "Test that TZID-qualified EXDATEs are converted to local time."
+  ;; Use a timezone different from local to verify conversion
+  ;; We'll use Europe/London and check that conversion happens
+  (let ((event "BEGIN:VEVENT
+DTSTART;TZID=Europe/London:20260203T130000
+RRULE:FREQ=WEEKLY;BYDAY=TU
+EXDATE;TZID=Europe/London:20260210T130000
+SUMMARY:London Meeting
+END:VEVENT"))
+    (let ((result (calendar-sync--collect-exdates event)))
+      (should (= 1 (length result)))
+      ;; Result should be a valid datetime list (conversion may differ based on local TZ)
+      (let ((parsed (car result)))
+        (should (= 5 (length parsed)))
+        (should (numberp (nth 0 parsed)))  ; year
+        (should (numberp (nth 1 parsed)))  ; month
+        (should (numberp (nth 2 parsed)))  ; day
+        (should (numberp (nth 3 parsed)))  ; hour
+        (should (numberp (nth 4 parsed))))))) ; minute
+
+;;; Boundary Cases
+
+(ert-deftest test-calendar-sync--collect-exdates-boundary-no-exdates-returns-empty ()
+  "Test that event without EXDATE returns empty list."
+  (let ((event "BEGIN:VEVENT
+DTSTART:20260203T130000
+RRULE:FREQ=WEEKLY;BYDAY=TU
+SUMMARY:Weekly Meeting
+END:VEVENT"))
+    (let ((result (calendar-sync--collect-exdates event)))
+      (should (listp result))
+      (should (= 0 (length result))))))
+
+(ert-deftest test-calendar-sync--collect-exdates-boundary-utc-converts-to-local ()
+  "Test that UTC (Z suffix) EXDATEs are converted to local time."
+  (let ((event "BEGIN:VEVENT
+DTSTART:20260203T180000Z
+RRULE:FREQ=WEEKLY;BYDAY=TU
+EXDATE:20260210T180000Z
+SUMMARY:UTC Meeting
+END:VEVENT"))
+    (let ((result (calendar-sync--collect-exdates event)))
+      (should (= 1 (length result)))
+      ;; Result should be converted to local time
+      (let ((parsed (car result)))
+        (should (= 5 (length parsed)))
+        ;; Date should be valid
+        (should (numberp (nth 0 parsed)))))))
+
+(ert-deftest test-calendar-sync--collect-exdates-boundary-mixed-formats-handles-all ()
+  "Test handling mix of TZID, UTC, and local time EXDATEs."
+  (let ((event "BEGIN:VEVENT
+DTSTART:20260203T130000
+RRULE:FREQ=WEEKLY;BYDAY=TU
+EXDATE:20260210T130000
+EXDATE:20260217T180000Z
+SUMMARY:Mixed Meeting
+END:VEVENT"))
+    (let ((result (calendar-sync--collect-exdates event)))
+      (should (= 2 (length result)))
+      ;; Both should be valid parsed datetimes
+      (dolist (parsed result)
+        (should (= 5 (length parsed)))
+        (should (numberp (nth 0 parsed)))))))
+
+(ert-deftest test-calendar-sync--collect-exdates-boundary-date-only-returns-date ()
+  "Test collecting all-day EXDATE returns date with nil for time."
+  (let ((event "BEGIN:VEVENT
+DTSTART;VALUE=DATE:20260203
+RRULE:FREQ=WEEKLY;BYDAY=TU
+EXDATE;VALUE=DATE:20260210
+SUMMARY:All Day Event
+END:VEVENT"))
+    (let ((result (calendar-sync--collect-exdates event)))
+      (should (= 1 (length result)))
+      (let ((parsed (car result)))
+        (should (equal '(2026 2 10 nil nil) parsed))))))
+
+;;; Error Cases
+
+(ert-deftest test-calendar-sync--collect-exdates-error-empty-string-returns-empty ()
+  "Test that empty string returns empty list."
+  (let ((result (calendar-sync--collect-exdates "")))
+    (should (listp result))
+    (should (= 0 (length result)))))
+
+(ert-deftest test-calendar-sync--collect-exdates-error-nil-returns-empty ()
+  "Test that nil input returns empty list."
+  (let ((result (calendar-sync--collect-exdates nil)))
+    (should (listp result))
+    (should (= 0 (length result)))))
+
+(ert-deftest test-calendar-sync--collect-exdates-error-malformed-returns-empty ()
+  "Test that malformed event returns empty list."
+  (let ((result (calendar-sync--collect-exdates "not a vevent")))
+    (should (listp result))
+    (should (= 0 (length result)))))
+
+(provide 'test-calendar-sync--collect-exdates)
+;;; test-calendar-sync--collect-exdates.el ends here