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+;;; test-keybindings--fullscreen.el --- F11 toggles frame fullscreen -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Stock Emacs binds F11 to `toggle-frame-fullscreen', the same key every
+;; other application on the desktop uses for it.  This config never rebound
+;; it; dirvish-config's :bind put dirvish-side on F11 and shadowed the stock
+;; binding for as long as that entry existed.  It moved to F9 on 2026-09-22
+;; (see test-dirvish-config--side-key.el, which pins the un-shadowing).
+;;
+;; These tests pin the foundation layer's side of that: keybindings.el must
+;; leave the stock F11 binding in place.  Only keybindings.el is loaded here
+;; on purpose.  A feature module that later claimed F11 would fail the
+;; dirvish-side regression test, not this one.
+
+;;; Code:
+
+(require 'ert)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'keybindings)
+
+;;; Normal
+
+(ert-deftest test-keybindings-f11-toggles-fullscreen ()
+  "Normal: F11 runs `toggle-frame-fullscreen' once the foundation layer has
+loaded.  Stock Emacs provides the binding; this pins that keybindings.el does
+not unset or rebind it."
+  (should (eq (keymap-lookup global-map "<f11>") #'toggle-frame-fullscreen)))
+
+;;; Boundary
+
+(ert-deftest test-keybindings-f11-is-the-only-fullscreen-chord ()
+  "Boundary: the plain key carries it; the shifted chord is left free so a
+grazed Shift does not toggle the frame twice."
+  (should-not (eq (keymap-lookup global-map "S-<f11>")
+                  #'toggle-frame-fullscreen)))
+
+;;; Error
+
+(ert-deftest test-keybindings-f11-target-is-a-command ()
+  "Error (positive control): the target is a real interactive command, so a
+press does not fail with a `commandp' error at press time."
+  (should (commandp (keymap-lookup global-map "<f11>"))))
+
+(provide 'test-keybindings--fullscreen)
+;;; test-keybindings--fullscreen.el ends here