refactor(dirvish): extract playlist filter and sanitize helpers

`cj/dired-create-playlist-from-marked' had its audio-file filtering and trailing-`.m3u' stripping inline among the dired marking, prompting, overwrite-loop, and file-write logic.  Lift each into its own pure helper:

- `cj/--playlist-filter-audio (files extensions)' returns only files whose extension matches one of EXTENSIONS (lowercase, no dot).  Case-insensitive on the file side.
- `cj/--playlist-sanitize-name (name)' strips a trailing `.m3u' suffix; embedded `.m3u' that isn't at the end is preserved.

Ten Normal/Boundary tests cover keep-only-audio, case-insensitivity, files-without-extension excluded, empty inputs, and the sanitize edge cases (bare name, embedded `.m3u', empty string, just `.m3u').

1 files changed, 82 insertions, 0 deletions

diff --git a/tests/test-dirvish-config-playlist.el b/tests/test-dirvish-config-playlist.el
new file mode 100644
index 00000000..3876a177
--- /dev/null
+++ b/tests/test-dirvish-config-playlist.el
@@ -0,0 +1,82 @@
+;;; test-dirvish-config-playlist.el --- Tests for the playlist helpers -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; `cj/--playlist-filter-audio' and `cj/--playlist-sanitize-name' are
+;; the two pure pieces under `cj/dired-create-playlist-from-marked'.
+;; The interactive command does the dired marking, prompting,
+;; overwrite-confirmation loop, and the file write -- the helpers stay
+;; testable in isolation.
+
+;;; Code:
+
+(require 'ert)
+(require 'package)
+
+(setq package-user-dir (expand-file-name "elpa" user-emacs-directory))
+(package-initialize)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(add-to-list 'load-path (expand-file-name "elpa/dirvish-2.3.0/extensions"
+                                          user-emacs-directory))
+(require 'user-constants)
+(require 'keybindings)
+(require 'dirvish-config)
+
+;;; --------------------------- filter-audio --------------------------
+
+(ert-deftest test-cj--playlist-filter-audio-keeps-only-audio ()
+  "Normal: a mixed list returns only the entries with audio extensions."
+  (should (equal (cj/--playlist-filter-audio
+                  '("/m/song.mp3" "/d/notes.org" "/m/track.flac" "/d/run.sh")
+                  '("mp3" "flac"))
+                 '("/m/song.mp3" "/m/track.flac"))))
+
+(ert-deftest test-cj--playlist-filter-audio-case-insensitive-extension ()
+  "Boundary: uppercase / mixed-case extensions are matched against the
+lowercase extension list."
+  (should (equal (cj/--playlist-filter-audio
+                  '("/m/A.MP3" "/m/B.Flac" "/m/c.OGG")
+                  '("mp3" "flac" "ogg"))
+                 '("/m/A.MP3" "/m/B.Flac" "/m/c.OGG"))))
+
+(ert-deftest test-cj--playlist-filter-audio-files-without-extension-excluded ()
+  "Boundary: a file with no extension can't be an audio file."
+  (should (equal (cj/--playlist-filter-audio
+                  '("/m/README" "/m/song.mp3" "/m/Makefile")
+                  '("mp3"))
+                 '("/m/song.mp3"))))
+
+(ert-deftest test-cj--playlist-filter-audio-empty-input-empty-output ()
+  "Boundary: no input files -> no output."
+  (should-not (cj/--playlist-filter-audio '() '("mp3" "flac"))))
+
+(ert-deftest test-cj--playlist-filter-audio-empty-extensions-empty-output ()
+  "Boundary: no allowed extensions -> nothing matches."
+  (should-not (cj/--playlist-filter-audio
+               '("/m/song.mp3" "/m/track.flac")
+               '())))
+
+;;; ---------------------- sanitize-playlist-name ---------------------
+
+(ert-deftest test-cj--playlist-sanitize-name-strips-trailing-m3u ()
+  "Normal: a `.m3u' suffix is stripped."
+  (should (equal (cj/--playlist-sanitize-name "summer.m3u") "summer")))
+
+(ert-deftest test-cj--playlist-sanitize-name-bare-name-unchanged ()
+  "Normal: a name without `.m3u' is returned unchanged."
+  (should (equal (cj/--playlist-sanitize-name "summer") "summer")))
+
+(ert-deftest test-cj--playlist-sanitize-name-embedded-m3u-untouched ()
+  "Boundary: `.m3u' that isn't at the end is kept (it's part of the name)."
+  (should (equal (cj/--playlist-sanitize-name "my.m3u.draft")
+                 "my.m3u.draft")))
+
+(ert-deftest test-cj--playlist-sanitize-name-empty-string-unchanged ()
+  "Boundary: empty string returns empty string."
+  (should (equal (cj/--playlist-sanitize-name "") "")))
+
+(ert-deftest test-cj--playlist-sanitize-name-only-suffix ()
+  "Boundary: a name that's just `.m3u' becomes empty after stripping."
+  (should (equal (cj/--playlist-sanitize-name ".m3u") "")))
+
+(provide 'test-dirvish-config-playlist)
+;;; test-dirvish-config-playlist.el ends here