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+;;; test-calendar-sync--helpers.el --- Tests for calendar-sync helper functions  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Unit tests for refactored helper functions.
+;; Tests the helper functions that simplify RRULE expansion logic.
+
+;;; Code:
+
+(require 'ert)
+(require 'calendar-sync)
+
+;;; Setup and Teardown
+
+(defun test-calendar-sync--helpers-setup ()
+  "Setup for helper function tests."
+  nil)
+
+(defun test-calendar-sync--helpers-teardown ()
+  "Teardown for helper function tests."
+  nil)
+
+;;; calendar-sync--date-to-time Tests
+
+(ert-deftest test-calendar-sync--date-to-time-converts-date-to-time ()
+  "Test converting date to time value."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let* ((date '(2025 11 18))  ; Nov 18, 2025
+             (time-val (calendar-sync--date-to-time date)))
+        ;; Should return a valid time value
+        (should (numberp (time-convert time-val 'integer))))
+    (test-calendar-sync--helpers-teardown)))
+
+(ert-deftest test-calendar-sync--date-to-time-handles-different-dates ()
+  "Test date-to-time with various dates."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let ((date1 '(2025 1 1))
+            (date2 '(2025 12 31)))
+        ;; Different dates should produce different time values
+        (should (not (equal (calendar-sync--date-to-time date1)
+                           (calendar-sync--date-to-time date2)))))
+    (test-calendar-sync--helpers-teardown)))
+
+;;; calendar-sync--before-date-p Tests
+
+(ert-deftest test-calendar-sync--before-date-p-returns-true-for-earlier-date ()
+  "Test that earlier dates return true."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let ((earlier '(2025 11 17))
+            (later '(2025 11 18)))
+        (should (calendar-sync--before-date-p earlier later)))
+    (test-calendar-sync--helpers-teardown)))
+
+(ert-deftest test-calendar-sync--before-date-p-returns-false-for-later-date ()
+  "Test that later dates return false."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let ((earlier '(2025 11 17))
+            (later '(2025 11 18)))
+        (should-not (calendar-sync--before-date-p later earlier)))
+    (test-calendar-sync--helpers-teardown)))
+
+(ert-deftest test-calendar-sync--before-date-p-returns-false-for-same-date ()
+  "Test that same dates return false."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let ((date '(2025 11 18)))
+        (should-not (calendar-sync--before-date-p date date)))
+    (test-calendar-sync--helpers-teardown)))
+
+(ert-deftest test-calendar-sync--before-date-p-handles-month-boundaries ()
+  "Test date comparison across month boundaries."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let ((november '(2025 11 30))
+            (december '(2025 12 1)))
+        (should (calendar-sync--before-date-p november december))
+        (should-not (calendar-sync--before-date-p december november)))
+    (test-calendar-sync--helpers-teardown)))
+
+(ert-deftest test-calendar-sync--before-date-p-handles-year-boundaries ()
+  "Test date comparison across year boundaries."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let ((dec-2025 '(2025 12 31))
+            (jan-2026 '(2026 1 1)))
+        (should (calendar-sync--before-date-p dec-2025 jan-2026))
+        (should-not (calendar-sync--before-date-p jan-2026 dec-2025)))
+    (test-calendar-sync--helpers-teardown)))
+
+;;; calendar-sync--create-occurrence Tests
+
+(ert-deftest test-calendar-sync--create-occurrence-creates-new-event ()
+  "Test creating occurrence from base event."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let* ((base-event '(:summary "Test Event"
+                          :start (2025 11 1 10 0 0)
+                          :end (2025 11 1 11 0 0)))
+             (new-date '(2025 11 15 10 0 0))
+             (occurrence (calendar-sync--create-occurrence base-event new-date)))
+        ;; Should have same summary
+        (should (equal (plist-get occurrence :summary) "Test Event"))
+        ;; Should have new start date
+        (should (equal (plist-get occurrence :start) new-date))
+        ;; Should have end date with same day as start
+        (let ((end (plist-get occurrence :end)))
+          (should (= (nth 0 end) 2025))
+          (should (= (nth 1 end) 11))
+          (should (= (nth 2 end) 15))))
+    (test-calendar-sync--helpers-teardown)))
+
+(ert-deftest test-calendar-sync--create-occurrence-preserves-time ()
+  "Test that occurrence preserves time from base event."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let* ((base-event '(:summary "Morning Meeting"
+                          :start (2025 11 1 9 30 0)
+                          :end (2025 11 1 10 30 0)))
+             (new-date '(2025 11 15 9 30 0))
+             (occurrence (calendar-sync--create-occurrence base-event new-date)))
+        ;; End time should preserve hours/minutes from base event
+        (let ((end (plist-get occurrence :end)))
+          (should (= (nth 3 end) 10))  ; hour
+          (should (= (nth 4 end) 30)))) ; minute
+    (test-calendar-sync--helpers-teardown)))
+
+(ert-deftest test-calendar-sync--create-occurrence-handles-no-end-time ()
+  "Test creating occurrence when base event has no end time."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let* ((base-event '(:summary "All Day Event"
+                          :start (2025 11 1 0 0 0)))
+             (new-date '(2025 11 15 0 0 0))
+             (occurrence (calendar-sync--create-occurrence base-event new-date)))
+        ;; Should have start but no end
+        (should (equal (plist-get occurrence :start) new-date))
+        (should (null (plist-get occurrence :end))))
+    (test-calendar-sync--helpers-teardown)))
+
+(ert-deftest test-calendar-sync--create-occurrence-does-not-modify-original ()
+  "Test that creating occurrence doesn't modify base event."
+  (test-calendar-sync--helpers-setup)
+  (unwind-protect
+      (let* ((original-start '(2025 11 1 10 0 0))
+             (base-event (list :summary "Test"
+                              :start original-start))
+             (new-date '(2025 11 15 10 0 0)))
+        (calendar-sync--create-occurrence base-event new-date)
+        ;; Original should be unchanged
+        (should (equal (plist-get base-event :start) original-start)))
+    (test-calendar-sync--helpers-teardown)))
+
+(provide 'test-calendar-sync--helpers)
+;;; test-calendar-sync--helpers.el ends here