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+;;; test-calendar-sync--parse-rrule.el --- Tests for calendar-sync--parse-rrule  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Unit tests for calendar-sync--parse-rrule function.
+;; Tests parsing of iCalendar RRULE strings into plist format.
+
+;;; Code:
+
+(require 'ert)
+(require 'calendar-sync)
+
+;;; Setup and Teardown
+
+(defun test-calendar-sync--parse-rrule-setup ()
+  "Setup for calendar-sync--parse-rrule tests."
+  ;; No setup required for pure parsing tests
+  nil)
+
+(defun test-calendar-sync--parse-rrule-teardown ()
+  "Teardown for calendar-sync--parse-rrule tests."
+  ;; No teardown required
+  nil)
+
+;;; Normal Cases
+
+(ert-deftest test-calendar-sync--parse-rrule-normal-weekly-returns-plist ()
+  "Test parsing simple weekly recurrence rule."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=WEEKLY")))
+        (should (eq (plist-get result :freq) 'weekly))
+        (should (= (plist-get result :interval) 1)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-normal-weekly-with-byday-returns-plist ()
+  "Test parsing weekly recurrence with specific weekdays."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=WEEKLY;BYDAY=SA")))
+        (should (eq (plist-get result :freq) 'weekly))
+        (should (equal (plist-get result :byday) '("SA")))
+        (should (= (plist-get result :interval) 1)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-normal-daily-returns-plist ()
+  "Test parsing daily recurrence rule."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=DAILY")))
+        (should (eq (plist-get result :freq) 'daily))
+        (should (= (plist-get result :interval) 1)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-normal-monthly-returns-plist ()
+  "Test parsing monthly recurrence rule."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=MONTHLY")))
+        (should (eq (plist-get result :freq) 'monthly))
+        (should (= (plist-get result :interval) 1)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-normal-yearly-returns-plist ()
+  "Test parsing yearly recurrence rule."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=YEARLY")))
+        (should (eq (plist-get result :freq) 'yearly))
+        (should (= (plist-get result :interval) 1)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-normal-with-interval-returns-plist ()
+  "Test parsing recurrence rule with custom interval."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=WEEKLY;INTERVAL=2")))
+        (should (eq (plist-get result :freq) 'weekly))
+        (should (= (plist-get result :interval) 2)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-normal-with-count-returns-plist ()
+  "Test parsing recurrence rule with count limit."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=DAILY;COUNT=10")))
+        (should (eq (plist-get result :freq) 'daily))
+        (should (= (plist-get result :count) 10)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-normal-with-until-returns-plist ()
+  "Test parsing recurrence rule with end date."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let* ((result (calendar-sync--parse-rrule "FREQ=WEEKLY;UNTIL=20261118T120000Z"))
+             (until (plist-get result :until)))
+        (should (eq (plist-get result :freq) 'weekly))
+        (should (listp until))
+        (should (= (nth 0 until) 2026))  ; year
+        (should (= (nth 1 until) 11))    ; month
+        ;; Day might be 17 or 18 depending on timezone conversion
+        (should (member (nth 2 until) '(17 18))))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+;;; Boundary Cases
+
+(ert-deftest test-calendar-sync--parse-rrule-boundary-multiple-byday-returns-list ()
+  "Test parsing BYDAY with multiple weekdays."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=WEEKLY;BYDAY=MO,WE,FR")))
+        (should (eq (plist-get result :freq) 'weekly))
+        (should (equal (plist-get result :byday) '("MO" "WE" "FR"))))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-boundary-all-parameters-returns-plist ()
+  "Test parsing RRULE with all supported parameters."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=WEEKLY;INTERVAL=2;BYDAY=SA;UNTIL=20261118T000000Z;COUNT=52")))
+        (should (eq (plist-get result :freq) 'weekly))
+        (should (= (plist-get result :interval) 2))
+        (should (equal (plist-get result :byday) '("SA")))
+        (should (plist-get result :until))
+        (should (= (plist-get result :count) 52)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-boundary-interval-one-returns-default ()
+  "Test that default interval is 1 when not specified."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=DAILY")))
+        (should (= (plist-get result :interval) 1)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-boundary-large-interval-returns-number ()
+  "Test parsing RRULE with large interval value."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=MONTHLY;INTERVAL=12")))
+        (should (= (plist-get result :interval) 12)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-boundary-large-count-returns-number ()
+  "Test parsing RRULE with large count value."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=DAILY;COUNT=365")))
+        (should (= (plist-get result :count) 365)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+;;; Error Cases
+
+(ert-deftest test-calendar-sync--parse-rrule-error-empty-string-returns-plist ()
+  "Test parsing empty RRULE string returns plist with defaults."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "")))
+        (should (listp result))
+        (should (= (plist-get result :interval) 1)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-error-unsupported-freq-returns-symbol ()
+  "Test parsing RRULE with unsupported frequency."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=HOURLY")))
+        (should (eq (plist-get result :freq) 'hourly)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-error-invalid-until-returns-nil ()
+  "Test parsing RRULE with malformed UNTIL date."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=DAILY;UNTIL=invalid")))
+        (should (eq (plist-get result :freq) 'daily))
+        (should (null (plist-get result :until))))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-error-invalid-count-returns-zero ()
+  "Test parsing RRULE with non-numeric COUNT."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=DAILY;COUNT=abc")))
+        (should (eq (plist-get result :freq) 'daily))
+        (should (= (plist-get result :count) 0)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-error-invalid-interval-returns-zero ()
+  "Test parsing RRULE with non-numeric INTERVAL."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "FREQ=WEEKLY;INTERVAL=xyz")))
+        (should (eq (plist-get result :freq) 'weekly))
+        (should (= (plist-get result :interval) 0)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(ert-deftest test-calendar-sync--parse-rrule-error-missing-freq-returns-plist ()
+  "Test parsing RRULE without FREQ parameter."
+  (test-calendar-sync--parse-rrule-setup)
+  (unwind-protect
+      (let ((result (calendar-sync--parse-rrule "INTERVAL=2;COUNT=10")))
+        (should (listp result))
+        (should (null (plist-get result :freq)))
+        (should (= (plist-get result :interval) 2))
+        (should (= (plist-get result :count) 10)))
+    (test-calendar-sync--parse-rrule-teardown)))
+
+(provide 'test-calendar-sync--parse-rrule)
+;;; test-calendar-sync--parse-rrule.el ends here