feat(music): add random-aware next/previous; refactor music + calendar-syncHEADmain

Music: random mode now respected by next/previous keys. Previous navigates
a 50-track play history ring buffer. Fixed playlist replacement bug.
24 new tests.

Calendar-sync: consolidated duplicate parse functions, extracted timezone
localization helper, unified expand-daily/monthly/yearly into parameterized
function, removed dead code. 33 new characterization tests. -90 lines.

1 files changed, 174 insertions, 0 deletions

diff --git a/tests/test-calendar-sync--expand-monthly.el b/tests/test-calendar-sync--expand-monthly.el
new file mode 100644
index 00000000..3dc1f2dc
--- /dev/null
+++ b/tests/test-calendar-sync--expand-monthly.el
@@ -0,0 +1,174 @@
+;;; test-calendar-sync--expand-monthly.el --- Tests for calendar-sync--expand-monthly  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Characterization tests for calendar-sync--expand-monthly.
+;; Captures current behavior before refactoring into unified expand function.
+;; Uses dynamic timestamps to avoid hardcoded dates.
+
+;;; Code:
+
+(require 'ert)
+(require 'testutil-calendar-sync)
+(require 'calendar-sync)
+
+;;; Normal Cases
+
+(ert-deftest test-calendar-sync--expand-monthly-normal-generates-occurrences ()
+  "Test expanding monthly event generates occurrences within range."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (end-date (test-calendar-sync-time-days-from-now 1 11 0))
+         (base-event (list :summary "Monthly Review"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    ;; ~12-15 months of range
+    (should (> (length occurrences) 10))
+    (should (< (length occurrences) 20))))
+
+(ert-deftest test-calendar-sync--expand-monthly-normal-preserves-day-of-month ()
+  "Test that each occurrence falls on the same day of month."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 5 10 0))
+         (end-date (test-calendar-sync-time-days-from-now 5 11 0))
+         (expected-day (nth 2 start-date))
+         (base-event (list :summary "Monthly"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    (should (> (length occurrences) 0))
+    ;; Day of month should be consistent (may clamp for short months)
+    (dolist (occ occurrences)
+      (let ((day (nth 2 (plist-get occ :start))))
+        (should (<= day expected-day))))))
+
+(ert-deftest test-calendar-sync--expand-monthly-normal-interval-two ()
+  "Test expanding bi-monthly event."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 9 0))
+         (end-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (base-event (list :summary "Bi-Monthly"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 2))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    ;; ~15 months / 2 = ~7-8 occurrences
+    (should (>= (length occurrences) 5))
+    (should (<= (length occurrences) 10))))
+
+(ert-deftest test-calendar-sync--expand-monthly-normal-preserves-time ()
+  "Test that each occurrence preserves the original event time."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 15 45))
+         (end-date (test-calendar-sync-time-days-from-now 1 16 45))
+         (base-event (list :summary "Timed Monthly"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1 :count 3))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    (dolist (occ occurrences)
+      (let ((s (plist-get occ :start)))
+        (should (= (nth 3 s) 15))
+        (should (= (nth 4 s) 45))))))
+
+;;; Boundary Cases
+
+(ert-deftest test-calendar-sync--expand-monthly-boundary-count-limits-occurrences ()
+  "Test that COUNT limits the total number of occurrences."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (end-date (test-calendar-sync-time-days-from-now 1 11 0))
+         (base-event (list :summary "Limited"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1 :count 4))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    (should (= (length occurrences) 4))))
+
+(ert-deftest test-calendar-sync--expand-monthly-boundary-until-limits-occurrences ()
+  "Test that UNTIL date stops expansion."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (end-date (test-calendar-sync-time-days-from-now 1 11 0))
+         (until-date (test-calendar-sync-time-date-only 120))
+         (base-event (list :summary "Until-Limited"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1 :until until-date))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    ;; ~4 months of monthly occurrences
+    (should (>= (length occurrences) 3))
+    (should (<= (length occurrences) 5))))
+
+(ert-deftest test-calendar-sync--expand-monthly-boundary-count-one-returns-single ()
+  "Test that COUNT=1 returns exactly one occurrence."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (end-date (test-calendar-sync-time-days-from-now 1 11 0))
+         (base-event (list :summary "Once"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1 :count 1))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    (should (= (length occurrences) 1))))
+
+(ert-deftest test-calendar-sync--expand-monthly-boundary-respects-date-range ()
+  "Test that occurrences outside date range are excluded."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (end-date (test-calendar-sync-time-days-from-now 1 11 0))
+         (base-event (list :summary "Ranged"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1))
+         (range (test-calendar-sync-narrow-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range))
+         (range-start (nth 0 range))
+         (range-end (nth 1 range)))
+    (dolist (occ occurrences)
+      (let* ((s (plist-get occ :start))
+             (occ-time (test-calendar-sync-date-to-time-value s)))
+        (should (time-less-p range-start occ-time))
+        (should (time-less-p occ-time range-end))))))
+
+(ert-deftest test-calendar-sync--expand-monthly-boundary-preserves-summary ()
+  "Test that each occurrence carries the original summary."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (end-date (test-calendar-sync-time-days-from-now 1 11 0))
+         (base-event (list :summary "Team Sync"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1 :count 3))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    (dolist (occ occurrences)
+      (should (equal (plist-get occ :summary) "Team Sync")))))
+
+;;; Error Cases
+
+(ert-deftest test-calendar-sync--expand-monthly-error-past-until-returns-empty ()
+  "Test that UNTIL in the past produces no occurrences in future range."
+  (let* ((start-date (test-calendar-sync-time-days-ago 200 10 0))
+         (end-date (test-calendar-sync-time-days-ago 200 11 0))
+         (until-date (test-calendar-sync-time-date-only-ago 100))
+         (base-event (list :summary "Past"
+                           :start start-date
+                           :end end-date))
+         (rrule (list :freq 'monthly :interval 1 :until until-date))
+         (range (list (time-subtract (current-time) (* 30 86400))
+                      (time-add (current-time) (* 365 86400))))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    (should (= (length occurrences) 0))))
+
+(ert-deftest test-calendar-sync--expand-monthly-error-no-end-time-still-works ()
+  "Test that event without :end still generates occurrences."
+  (let* ((start-date (test-calendar-sync-time-days-from-now 1 10 0))
+         (base-event (list :summary "No End" :start start-date))
+         (rrule (list :freq 'monthly :interval 1 :count 3))
+         (range (test-calendar-sync-wide-range))
+         (occurrences (calendar-sync--expand-monthly base-event rrule range)))
+    (should (= (length occurrences) 3))))
+
+(provide 'test-calendar-sync--expand-monthly)
+;;; test-calendar-sync--expand-monthly.el ends here