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, 54 insertions, 0 deletions

diff --git a/tests/test-calendar-sync--localize-parsed-datetime.el b/tests/test-calendar-sync--localize-parsed-datetime.el
new file mode 100644
index 00000000..ef9cf099
--- /dev/null
+++ b/tests/test-calendar-sync--localize-parsed-datetime.el
@@ -0,0 +1,54 @@
+;;; test-calendar-sync--localize-parsed-datetime.el --- Tests for datetime localization -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for calendar-sync--localize-parsed-datetime.
+;; Dispatches to UTC or TZID conversion, or passes through unchanged.
+
+;;; Code:
+
+(require 'ert)
+(require 'testutil-calendar-sync)
+(require 'calendar-sync)
+
+;;; Normal Cases
+
+(ert-deftest test-calendar-sync--localize-parsed-datetime-normal-utc ()
+  "UTC flag triggers conversion via convert-utc-to-local."
+  (let ((parsed '(2026 3 15 18 0)))
+    (let ((result (calendar-sync--localize-parsed-datetime parsed t nil)))
+      (should (= 5 (length result)))
+      ;; Hour should differ from 18 unless we're in UTC
+      (let ((tz-offset (car (current-time-zone))))
+        (unless (= tz-offset 0)
+          (should-not (= 18 (nth 3 result))))))))
+
+(ert-deftest test-calendar-sync--localize-parsed-datetime-normal-tzid ()
+  "TZID triggers conversion via convert-tz-to-local."
+  (let ((parsed '(2026 3 15 14 0)))
+    (let ((result (calendar-sync--localize-parsed-datetime parsed nil "America/New_York")))
+      (should (= 5 (length result))))))
+
+(ert-deftest test-calendar-sync--localize-parsed-datetime-normal-local-passthrough ()
+  "No UTC, no TZID — returns parsed unchanged."
+  (let ((parsed '(2026 3 15 14 0)))
+    (should (equal parsed (calendar-sync--localize-parsed-datetime parsed nil nil)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-calendar-sync--localize-parsed-datetime-boundary-date-only ()
+  "Date-only (nil hour/minute) with UTC uses 0 for time components."
+  (let ((parsed '(2026 3 15 nil nil)))
+    (let ((result (calendar-sync--localize-parsed-datetime parsed t nil)))
+      (should (= 5 (length result))))))
+
+;;; Error Cases
+
+(ert-deftest test-calendar-sync--localize-parsed-datetime-error-bad-tzid-fallback ()
+  "Invalid TZID falls back to returning parsed unchanged."
+  (let ((parsed '(2026 3 15 14 0)))
+    (let ((result (calendar-sync--localize-parsed-datetime parsed nil "Fake/Timezone")))
+      ;; convert-tz-to-local returns nil for bad TZID, so fallback to parsed
+      (should (= 5 (length result))))))
+
+(provide 'test-calendar-sync--localize-parsed-datetime)
+;;; test-calendar-sync--localize-parsed-datetime.el ends here