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+;;; test-ai-term--display-rule.el --- Tests for the AI-term display-buffer rule -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; The module installs a `display-buffer-alist' entry routing buffers
+;; whose names match "\\`agent \\[" to a right-side window.  These
+;; tests verify the rule reaches the right side and ignores buffers
+;; that don't match the prefix.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'ai-term)
+
+(defun test-ai-term--cleanup (name)
+  "Kill buffer NAME if it exists."
+  (when (get-buffer name)
+    (kill-buffer name)))
+
+(defmacro test-ai-term--with-clean-frame (&rest body)
+  "Run BODY in a context with one window and the AI-term rule loaded."
+  (declare (indent 0) (debug t))
+  `(save-window-excursion
+     (delete-other-windows)
+     (let ((display-buffer-alist (cj/--ai-term-display-rule-list)))
+       ,@body)))
+
+(ert-deftest test-ai-term--display-rule-routes-agent-buffer-to-right ()
+  "Normal: on a desktop, \"agent [foo]\" lands in a window to the right.
+
+The desktop default direction is `right' (see
+`cj/--ai-term-default-direction'), so the rule splits the current
+window with `(direction . right)' and the new window's left edge
+sits at a positive column.  `env-laptop-p' is stubbed nil to pin the
+desktop branch; on a laptop the agent would land below instead."
+  (let ((name "agent [display-rule-test]"))
+    (test-ai-term--cleanup name)
+    (unwind-protect
+        (cl-letf (((symbol-function 'env-laptop-p) (lambda () nil)))
+          (test-ai-term--with-clean-frame
+            (let* ((buf (get-buffer-create name))
+                   (win (display-buffer buf)))
+              (should (windowp win))
+              (should (> (window-left-column win) 0)))))
+      (test-ai-term--cleanup name))))
+
+(ert-deftest test-ai-term--display-rule-skips-non-matching-buffer ()
+  "Boundary: a buffer not named \"agent [...]\" does not match the rule.
+
+The rule's regex doesn't fire, so `display-buffer' falls back to the
+default action -- reuse the current window -- and no rightward split
+occurs."
+  (let ((name "scratch-buffer-no-match"))
+    (test-ai-term--cleanup name)
+    (unwind-protect
+        (test-ai-term--with-clean-frame
+          (let* ((buf (get-buffer-create name))
+                 (win (display-buffer buf)))
+            (should (windowp win))
+            (should (= (window-left-column win) 0))))
+      (test-ai-term--cleanup name))))
+
+(ert-deftest test-ai-term--display-rule-prefix-not-substring ()
+  "Boundary: \"foo agent [bar]\" does not match -- the rule anchors at start."
+  (let ((name "foo agent [substring-test]"))
+    (test-ai-term--cleanup name)
+    (unwind-protect
+        (test-ai-term--with-clean-frame
+          (let* ((buf (get-buffer-create name))
+                 (win (display-buffer buf)))
+            (should (windowp win))
+            (should (= (window-left-column win) 0))))
+      (test-ai-term--cleanup name))))
+
+(provide 'test-ai-term--display-rule)
+;;; test-ai-term--display-rule.el ends here