test(calendar-sync): add 68 tests across 13 files for untested pure functions

Covers core parsing (parse-ics-datetime, parse-timestamp, format-timestamp,
split-events, parse-event), date utilities (add-months, add-days,
weekday-to-number, date-weekday, event-start-time), and timezone
(format-timezone-offset, convert-utc-to-local, localize-parsed-datetime).

1 files changed, 53 insertions, 0 deletions

diff --git a/tests/test-calendar-sync--parse-ics-datetime.el b/tests/test-calendar-sync--parse-ics-datetime.el
new file mode 100644
index 00000000..6f1c083b
--- /dev/null
+++ b/tests/test-calendar-sync--parse-ics-datetime.el
@@ -0,0 +1,53 @@
+;;; test-calendar-sync--parse-ics-datetime.el --- Tests for iCal datetime parser -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for calendar-sync--parse-ics-datetime.
+;; Covers three formats: UTC datetime (Z suffix), local datetime, date-only.
+
+;;; Code:
+
+(require 'ert)
+(require 'testutil-calendar-sync)
+(require 'calendar-sync)
+
+;;; Normal Cases
+
+(ert-deftest test-calendar-sync--parse-ics-datetime-normal-utc ()
+  "UTC datetime (Z suffix) returns (year month day hour minute)."
+  (let ((result (calendar-sync--parse-ics-datetime "20260203T090000Z")))
+    (should (equal '(2026 2 3 9 0) result))))
+
+(ert-deftest test-calendar-sync--parse-ics-datetime-normal-local ()
+  "Local datetime (no Z) returns (year month day hour minute)."
+  (let ((result (calendar-sync--parse-ics-datetime "20260315T143000")))
+    (should (equal '(2026 3 15 14 30) result))))
+
+(ert-deftest test-calendar-sync--parse-ics-datetime-normal-date-only ()
+  "Date-only returns (year month day nil nil)."
+  (let ((result (calendar-sync--parse-ics-datetime "20260203")))
+    (should (equal '(2026 2 3 nil nil) result))))
+
+;;; Boundary Cases
+
+(ert-deftest test-calendar-sync--parse-ics-datetime-boundary-midnight ()
+  "Midnight is parsed as hour 0, minute 0."
+  (let ((result (calendar-sync--parse-ics-datetime "20260101T000000Z")))
+    (should (equal '(2026 1 1 0 0) result))))
+
+(ert-deftest test-calendar-sync--parse-ics-datetime-boundary-end-of-day ()
+  "23:59 is parsed correctly."
+  (let ((result (calendar-sync--parse-ics-datetime "20261231T235900")))
+    (should (equal '(2026 12 31 23 59) result))))
+
+;;; Error Cases
+
+(ert-deftest test-calendar-sync--parse-ics-datetime-error-nil ()
+  "Nil input returns nil."
+  (should (null (calendar-sync--parse-ics-datetime nil))))
+
+(ert-deftest test-calendar-sync--parse-ics-datetime-error-empty-string ()
+  "Empty string returns nil."
+  (should (null (calendar-sync--parse-ics-datetime ""))))
+
+(provide 'test-calendar-sync--parse-ics-datetime)
+;;; test-calendar-sync--parse-ics-datetime.el ends here