refactor(dirvish): extract cj/--wallpaper-program-for helper

`cj/set-wallpaper' had two parallel cond arms hardcoding the X11/Wayland dispatch and the success/failure messages inline.  Lift the program-and-args choice into `cj/--wallpaper-program-for' -- a pcase from a display-server symbol to a (PROGRAM ARG...) list, or nil for unknown environments.  The wrapper now: detect env, ask helper for the command, surface the right message (unknown server / executable missing / success).  Adding a third backend (e.g. xdg-desktop-portal) becomes one pcase clause + one test.

1 files changed, 42 insertions, 0 deletions

diff --git a/tests/test-dirvish-config-wallpaper-program.el b/tests/test-dirvish-config-wallpaper-program.el
new file mode 100644
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+++ b/tests/test-dirvish-config-wallpaper-program.el
@@ -0,0 +1,42 @@
+;;; test-dirvish-config-wallpaper-program.el --- Tests for the wallpaper command resolver -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; `cj/--wallpaper-program-for' is the pure dispatch behind
+;; `cj/set-wallpaper': given a display-server symbol it returns the
+;; (PROGRAM . PRE-FILE-ARGS) cons that the interactive wrapper passes
+;; to `call-process' alongside the wallpaper file path.  The wrapper
+;; handles environment detection (`env-x11-p' / `env-wayland-p'), the
+;; `executable-find' check, and the user-visible message.
+
+;;; 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)
+
+(ert-deftest test-cj--wallpaper-program-for-x11 ()
+  "Normal: x11 dispatches to feh with --bg-fill."
+  (should (equal (cj/--wallpaper-program-for 'x11)
+                 '("feh" "--bg-fill"))))
+
+(ert-deftest test-cj--wallpaper-program-for-wayland ()
+  "Normal: wayland dispatches to swww with the img subcommand."
+  (should (equal (cj/--wallpaper-program-for 'wayland)
+                 '("swww" "img"))))
+
+(ert-deftest test-cj--wallpaper-program-for-unknown-returns-nil ()
+  "Boundary: an unknown environment returns nil so the wrapper can fall back."
+  (should-not (cj/--wallpaper-program-for 'tty))
+  (should-not (cj/--wallpaper-program-for nil))
+  (should-not (cj/--wallpaper-program-for 'mac)))
+
+(provide 'test-dirvish-config-wallpaper-program)
+;;; test-dirvish-config-wallpaper-program.el ends here