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+;;; test-music-config--assert-valid-playlist-file.el --- Tests for playlist file validation -*- coding: utf-8; lexical-binding: t; -*-
+;;
+;; Author: Craig Jennings <c@cjennings.net>
+;;
+;;; Commentary:
+;; Unit tests for cj/music--assert-valid-playlist-file function.
+;; Tests the validation guard that ensures a playlist buffer has
+;; a valid, existing associated M3U file before operations proceed.
+;;
+;; Test organization:
+;; - Normal Cases: Valid file passes without error
+;; - Boundary Cases: Empty file, file exists but is empty
+;; - Error Cases: Nil file, nonexistent file, deleted file
+;;
+;;; Code:
+
+(require 'ert)
+(require 'testutil-general)
+
+;; 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-assert--setup ()
+  "Create test base dir and ensure playlist buffer exists."
+  (cj/create-test-base-dir)
+  (let ((buf (get-buffer-create cj/music-playlist-buffer-name)))
+    (with-current-buffer buf
+      (emms-playlist-mode)
+      (setq emms-playlist-buffer-p t))
+    (setq emms-playlist-buffer buf)
+    buf))
+
+(defun test-assert--teardown ()
+  "Clean up test playlist buffer and temp files."
+  (when-let ((buf (get-buffer cj/music-playlist-buffer-name)))
+    (with-current-buffer buf
+      (setq cj/music-playlist-file nil))
+    (kill-buffer buf))
+  (cj/delete-test-base-dir))
+
+;;; Normal Cases
+
+(ert-deftest test-music-config--assert-valid-playlist-file-normal-existing-file-passes ()
+  "Valid existing file does not signal error."
+  (test-assert--setup)
+  (unwind-protect
+      (let ((file (cj/create-temp-test-file "playlist-")))
+        (with-current-buffer (get-buffer cj/music-playlist-buffer-name)
+          (setq cj/music-playlist-file file))
+        ;; Should not error
+        (cj/music--assert-valid-playlist-file))
+    (test-assert--teardown)))
+
+(ert-deftest test-music-config--assert-valid-playlist-file-normal-file-with-content-passes ()
+  "Valid file with content does not signal error."
+  (test-assert--setup)
+  (unwind-protect
+      (let ((file (cj/create-temp-test-file-with-content "track1.mp3\ntrack2.mp3\n" "playlist-")))
+        (with-current-buffer (get-buffer cj/music-playlist-buffer-name)
+          (setq cj/music-playlist-file file))
+        (cj/music--assert-valid-playlist-file))
+    (test-assert--teardown)))
+
+;;; Boundary Cases
+
+(ert-deftest test-music-config--assert-valid-playlist-file-boundary-empty-file-passes ()
+  "Empty but existing file does not signal error."
+  (test-assert--setup)
+  (unwind-protect
+      (let ((file (cj/create-temp-test-file "playlist-")))
+        (with-current-buffer (get-buffer cj/music-playlist-buffer-name)
+          (setq cj/music-playlist-file file))
+        ;; File exists but is empty - should still pass
+        (cj/music--assert-valid-playlist-file))
+    (test-assert--teardown)))
+
+;;; Error Cases
+
+(ert-deftest test-music-config--assert-valid-playlist-file-error-nil-file-signals-user-error ()
+  "Nil cj/music-playlist-file signals user-error."
+  (test-assert--setup)
+  (unwind-protect
+      (progn
+        (with-current-buffer (get-buffer cj/music-playlist-buffer-name)
+          (setq cj/music-playlist-file nil))
+        (should-error (cj/music--assert-valid-playlist-file)
+                      :type 'user-error))
+    (test-assert--teardown)))
+
+(ert-deftest test-music-config--assert-valid-playlist-file-error-nonexistent-file-signals-user-error ()
+  "Nonexistent file path signals user-error."
+  (test-assert--setup)
+  (unwind-protect
+      (progn
+        (with-current-buffer (get-buffer cj/music-playlist-buffer-name)
+          (setq cj/music-playlist-file "/nonexistent/path/to/playlist.m3u"))
+        (should-error (cj/music--assert-valid-playlist-file)
+                      :type 'user-error))
+    (test-assert--teardown)))
+
+(ert-deftest test-music-config--assert-valid-playlist-file-error-deleted-file-signals-user-error ()
+  "File that existed but was deleted signals user-error."
+  (test-assert--setup)
+  (unwind-protect
+      (let ((file (cj/create-temp-test-file "playlist-")))
+        (with-current-buffer (get-buffer cj/music-playlist-buffer-name)
+          (setq cj/music-playlist-file file))
+        ;; Verify it passes first
+        (cj/music--assert-valid-playlist-file)
+        ;; Now delete the file
+        (delete-file file)
+        ;; Should now signal error
+        (should-error (cj/music--assert-valid-playlist-file)
+                      :type 'user-error))
+    (test-assert--teardown)))
+
+(provide 'test-music-config--assert-valid-playlist-file)
+;;; test-music-config--assert-valid-playlist-file.el ends here