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+;;; test-nerd-icons-config--color-dir.el --- Tests for cj/--nerd-icons-color-dir -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the :filter-return advice that attaches a color face to the
+;; output of `nerd-icons-icon-for-dir'. Without this, directory icons render
+;; in the buffer default face — so a face-remap of `default' (buffer-local
+;; or global) catches the icons unintentionally.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'nerd-icons-config)
+
+(ert-deftest test-nerd-icons-config--color-dir-attaches-face ()
+  "Normal: adds nerd-icons-yellow to the face stack of a propertized icon."
+  (let ((icon (propertize "X" 'face '(:family "Symbols Nerd Font Mono" :height 1.0))))
+    (let ((result (cj/--nerd-icons-color-dir icon)))
+      (should (memq 'nerd-icons-yellow
+                    (ensure-list (get-text-property 0 'face result)))))))
+
+(ert-deftest test-nerd-icons-config--color-dir-preserves-family ()
+  "Normal: retains the original :family / :height attributes."
+  (let ((icon (propertize "X" 'face '(:family "Symbols Nerd Font Mono" :height 1.0))))
+    (let* ((result (cj/--nerd-icons-color-dir icon))
+           (face   (get-text-property 0 'face result))
+           (specs  (ensure-list face))
+           (plist  (seq-find (lambda (x) (and (listp x) (plist-member x :family))) specs)))
+      (should (equal (plist-get plist :family) "Symbols Nerd Font Mono"))
+      (should (equal (plist-get plist :height) 1.0)))))
+
+(ert-deftest test-nerd-icons-config--color-dir-empty-string ()
+  "Boundary: an empty icon string returns unchanged (no range to propertize)."
+  (let ((icon ""))
+    (should (equal (cj/--nerd-icons-color-dir icon) ""))))
+
+(ert-deftest test-nerd-icons-config--color-dir-non-string-passthrough ()
+  "Error: a nil input returns nil rather than erroring."
+  (should-not (cj/--nerd-icons-color-dir nil)))
+
+(ert-deftest test-nerd-icons-config--color-dir-idempotent ()
+  "Boundary: calling twice on the same icon adds the face only once.
+nerd-icons memoizes its return strings — without this guard, repeated
+renders would stack `nerd-icons-yellow' over and over on the cached string."
+  (let ((icon (propertize "X" 'face '(:family "Symbols Nerd Font Mono" :height 1.0))))
+    (cj/--nerd-icons-color-dir icon)
+    (cj/--nerd-icons-color-dir icon)
+    (cj/--nerd-icons-color-dir icon)
+    (let* ((face (get-text-property 0 'face icon))
+           (specs (ensure-list face))
+           (yellows (cl-count 'nerd-icons-yellow specs)))
+      (should (= yellows 1)))))
+
+(provide 'test-nerd-icons-config--color-dir)
+;;; test-nerd-icons-config--color-dir.el ends here