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+;;; test-ai-term--next-agent-buffer.el --- Tests for cj/--ai-term-next-agent-buffer -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; The pure decision helper behind `cj/ai-term-next' (s-F9).  Given the
+;; current agent buffer and the ordered list of live agent buffers, it
+;; returns the next buffer in the queue, wrapping after the last.  A nil
+;; or non-member CURRENT returns the first; an empty list returns nil.
+;; No buffer or window side effects -- list logic only.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'ai-term)
+
+(ert-deftest test-ai-term--next-agent-buffer-advances-from-first ()
+  "Normal: current is the first element -> returns the second."
+  (let ((a (get-buffer-create "agent [a]"))
+        (b (get-buffer-create "agent [b]"))
+        (c (get-buffer-create "agent [c]")))
+    (unwind-protect
+        (should (eq b (cj/--ai-term-next-agent-buffer a (list a b c))))
+      (mapc #'kill-buffer (list a b c)))))
+
+(ert-deftest test-ai-term--next-agent-buffer-advances-from-middle ()
+  "Normal: current in the middle -> returns the following element."
+  (let ((a (get-buffer-create "agent [a]"))
+        (b (get-buffer-create "agent [b]"))
+        (c (get-buffer-create "agent [c]")))
+    (unwind-protect
+        (should (eq c (cj/--ai-term-next-agent-buffer b (list a b c))))
+      (mapc #'kill-buffer (list a b c)))))
+
+(ert-deftest test-ai-term--next-agent-buffer-wraps-after-last ()
+  "Boundary: current is the last element -> wraps to the first."
+  (let ((a (get-buffer-create "agent [a]"))
+        (b (get-buffer-create "agent [b]"))
+        (c (get-buffer-create "agent [c]")))
+    (unwind-protect
+        (should (eq a (cj/--ai-term-next-agent-buffer c (list a b c))))
+      (mapc #'kill-buffer (list a b c)))))
+
+(ert-deftest test-ai-term--next-agent-buffer-single-element-returns-itself ()
+  "Boundary: a one-agent queue wraps current back to itself."
+  (let ((a (get-buffer-create "agent [a]")))
+    (unwind-protect
+        (should (eq a (cj/--ai-term-next-agent-buffer a (list a))))
+      (kill-buffer a))))
+
+(ert-deftest test-ai-term--next-agent-buffer-nil-current-returns-first ()
+  "Boundary: nil current (no agent displayed) -> returns the first."
+  (let ((a (get-buffer-create "agent [a]"))
+        (b (get-buffer-create "agent [b]")))
+    (unwind-protect
+        (should (eq a (cj/--ai-term-next-agent-buffer nil (list a b))))
+      (mapc #'kill-buffer (list a b)))))
+
+(ert-deftest test-ai-term--next-agent-buffer-non-member-current-returns-first ()
+  "Error: current not in the queue -> returns the first rather than nil."
+  (let ((a (get-buffer-create "agent [a]"))
+        (b (get-buffer-create "agent [b]"))
+        (stray (get-buffer-create "agent [stray]")))
+    (unwind-protect
+        (should (eq a (cj/--ai-term-next-agent-buffer stray (list a b))))
+      (mapc #'kill-buffer (list a b stray)))))
+
+(ert-deftest test-ai-term--next-agent-buffer-empty-queue-returns-nil ()
+  "Boundary: an empty queue returns nil (nothing to switch to)."
+  (should (null (cj/--ai-term-next-agent-buffer nil '()))))
+
+(provide 'test-ai-term--next-agent-buffer)
+;;; test-ai-term--next-agent-buffer.el ends here