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+;;; test-music-config--ensure-playlist-buffer.el --- Tests for playlist buffer creation -*- coding: utf-8; lexical-binding: t; -*-
+;;
+;; Author: Craig Jennings <c@cjennings.net>
+;;
+;;; Commentary:
+;; Unit tests for cj/music--ensure-playlist-buffer function.
+;; Tests buffer creation, mode setup, and global variable assignment.
+;;
+;; Test organization:
+;; - Normal Cases: Creates new buffer, returns existing buffer
+;; - Boundary Cases: Wrong mode gets corrected, sets global variable
+;; - Error Cases: Killed buffer gets recreated, returns live buffer
+;;
+;;; Code:
+
+(require 'ert)
+
+;; Stub missing dependencies before loading music-config
+(defvar-keymap cj/custom-keymap
+  :doc "Stub keymap for testing")
+
+;; Add EMMS elpa directory to load path for batch testing
+(let ((emms-dir (car (file-expand-wildcards
+                      (expand-file-name "elpa/emms-*" user-emacs-directory)))))
+  (when emms-dir
+    (add-to-list 'load-path emms-dir)))
+
+(require 'emms)
+(require 'emms-playlist-mode)
+(require 'music-config)
+
+;;; Test helpers
+
+(defun test-ensure--teardown ()
+  "Clean up test playlist buffer."
+  (when-let ((buf (get-buffer cj/music-playlist-buffer-name)))
+    (kill-buffer buf)))
+
+;;; Normal Cases
+
+(ert-deftest test-music-config--ensure-playlist-buffer-normal-creates-buffer-when-none-exists ()
+  "Creates a new playlist buffer when none exists."
+  (unwind-protect
+      (progn
+        ;; Kill any existing buffer
+        (when-let ((buf (get-buffer cj/music-playlist-buffer-name)))
+          (kill-buffer buf))
+        (let ((result (cj/music--ensure-playlist-buffer)))
+          (should (bufferp result))
+          (should (buffer-live-p result))
+          (should (equal (buffer-name result) cj/music-playlist-buffer-name))))
+    (test-ensure--teardown)))
+
+(ert-deftest test-music-config--ensure-playlist-buffer-normal-returns-existing-buffer ()
+  "Returns existing buffer without recreating it."
+  (unwind-protect
+      (let* ((buf1 (cj/music--ensure-playlist-buffer))
+             (buf2 (cj/music--ensure-playlist-buffer)))
+        (should (eq buf1 buf2)))
+    (test-ensure--teardown)))
+
+;;; Boundary Cases
+
+(ert-deftest test-music-config--ensure-playlist-buffer-boundary-wrong-mode-corrected ()
+  "Buffer in wrong mode gets corrected to emms-playlist-mode."
+  (unwind-protect
+      (progn
+        ;; Create buffer in fundamental-mode
+        (let ((buf (get-buffer-create cj/music-playlist-buffer-name)))
+          (with-current-buffer buf
+            (fundamental-mode)))
+        (let ((result (cj/music--ensure-playlist-buffer)))
+          (with-current-buffer result
+            (should (eq major-mode 'emms-playlist-mode)))))
+    (test-ensure--teardown)))
+
+(ert-deftest test-music-config--ensure-playlist-buffer-boundary-sets-global-variable ()
+  "Sets emms-playlist-buffer to the returned buffer."
+  (unwind-protect
+      (let ((result (cj/music--ensure-playlist-buffer)))
+        (should (eq emms-playlist-buffer result)))
+    (test-ensure--teardown)))
+
+(ert-deftest test-music-config--ensure-playlist-buffer-boundary-sets-buffer-local-flag ()
+  "Sets emms-playlist-buffer-p to t in the buffer."
+  (unwind-protect
+      (let ((result (cj/music--ensure-playlist-buffer)))
+        (with-current-buffer result
+          (should (eq emms-playlist-buffer-p t))))
+    (test-ensure--teardown)))
+
+;;; Error Cases
+
+(ert-deftest test-music-config--ensure-playlist-buffer-error-killed-buffer-recreated ()
+  "After buffer is killed, calling again creates a new live buffer."
+  (unwind-protect
+      (progn
+        (let ((buf1 (cj/music--ensure-playlist-buffer)))
+          (kill-buffer buf1))
+        (let ((buf2 (cj/music--ensure-playlist-buffer)))
+          (should (buffer-live-p buf2))
+          (should (equal (buffer-name buf2) cj/music-playlist-buffer-name))))
+    (test-ensure--teardown)))
+
+(provide 'test-music-config--ensure-playlist-buffer)
+;;; test-music-config--ensure-playlist-buffer.el ends here