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+;;; test-dev-fkeys--f4-project-root.el --- Tests for cj/--f4-project-root -*- lexical-binding: t -*-
+
+;;; Commentary:
+;; Tests for the projectile-root wrapper. Projectile's
+;; `projectile-project-root' raises an error in some configurations when
+;; called outside a known project; this wrapper degrades to nil so the F4
+;; dispatcher can route to the 'unknown branch instead of crashing.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'dev-fkeys)
+
+;;; Normal Cases
+
+(ert-deftest test-dev-fkeys-f4-project-root-returns-projectile-value ()
+  "Normal: returns whatever `projectile-project-root' returns when fbound."
+  (cl-letf (((symbol-function 'projectile-project-root)
+             (lambda () "/some/project/")))
+    (should (string= (cj/--f4-project-root) "/some/project/"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-dev-fkeys-f4-project-root-returns-nil-when-projectile-unbound ()
+  "Boundary: returns nil when projectile is not loaded.
+
+Components integrated:
+- `cj/--f4-project-root' (unit under test)
+- `projectile-project-root' (MOCKED — fmakunbound to simulate absence)"
+  (let ((had-projectile (fboundp 'projectile-project-root))
+        (saved (and (fboundp 'projectile-project-root)
+                    (symbol-function 'projectile-project-root))))
+    (unwind-protect
+        (progn
+          (when had-projectile (fmakunbound 'projectile-project-root))
+          (should (null (cj/--f4-project-root))))
+      (when had-projectile
+        (fset 'projectile-project-root saved)))))
+
+;;; Error Cases
+
+(ert-deftest test-dev-fkeys-f4-project-root-returns-nil-on-projectile-error ()
+  "Error: returns nil when `projectile-project-root' signals an error."
+  (cl-letf (((symbol-function 'projectile-project-root)
+             (lambda () (error "Outside a known project"))))
+    (should (null (cj/--f4-project-root)))))
+
+(provide 'test-dev-fkeys--f4-project-root)
+;;; test-dev-fkeys--f4-project-root.el ends here