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, 37 insertions, 0 deletions

diff --git a/tests/test-calendar-sync--weekday-to-number.el b/tests/test-calendar-sync--weekday-to-number.el
new file mode 100644
index 00000000..bcad7917
--- /dev/null
+++ b/tests/test-calendar-sync--weekday-to-number.el
@@ -0,0 +1,37 @@
+;;; test-calendar-sync--weekday-to-number.el --- Tests for weekday mapping -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for calendar-sync--weekday-to-number. Pure string→number mapping.
+
+;;; Code:
+
+(require 'ert)
+(require 'testutil-calendar-sync)
+(require 'calendar-sync)
+
+;;; Normal Cases
+
+(ert-deftest test-calendar-sync--weekday-to-number-normal-monday ()
+  "MO maps to 1."
+  (should (= 1 (calendar-sync--weekday-to-number "MO"))))
+
+(ert-deftest test-calendar-sync--weekday-to-number-normal-all-days ()
+  "All seven days map to 1-7."
+  (should (equal '(1 2 3 4 5 6 7)
+                 (mapcar #'calendar-sync--weekday-to-number
+                         '("MO" "TU" "WE" "TH" "FR" "SA" "SU")))))
+
+;;; Boundary Cases
+
+(ert-deftest test-calendar-sync--weekday-to-number-boundary-sunday ()
+  "SU maps to 7 (not 0)."
+  (should (= 7 (calendar-sync--weekday-to-number "SU"))))
+
+;;; Error Cases
+
+(ert-deftest test-calendar-sync--weekday-to-number-error-invalid ()
+  "Invalid weekday string returns nil."
+  (should (null (calendar-sync--weekday-to-number "XX"))))
+
+(provide 'test-calendar-sync--weekday-to-number)
+;;; test-calendar-sync--weekday-to-number.el ends here