refactor(tests): extract shared buffer-cleanup and fake-vterm helpers

Eight test files across the ai-vterm and vterm-toggle suites each shipped a small variant of the same cleanup loop: walk `buffer-list`, kill any buffer whose name starts with a given prefix. Each file also re-implemented the `(string-prefix-p ...)` check inline. One file additionally had its own fake-vterm-mode-buffer constructor for tests that needed `cj/--vterm-toggle-buffer-p` to fire.

I pulled the shared logic into `tests/testutil-vterm-buffers.el`:

- `cj/test--kill-buffers-matching-prefix` is the primitive.
- `cj/test--kill-claude-buffers` and `cj/test--kill-test-vterm-buffers` are thin wrappers for the two prefixes that actually appear.
- `cj/test--make-fake-vterm-buffer` constructs a buffer with `major-mode` set to `vterm-mode` without launching a real vterm process.

Each affected test file now `(require 'testutil-vterm-buffers)` and calls the shared helpers directly. `test-vterm-toggle--buffer-filter.el` keeps a 3-line wrapper that calls both kill helpers in sequence (the only place that needs both prefixes). Net diff: -116 / +72 across 8 test files, plus ~30 lines in the new testutil. Roughly -45 lines after the abstraction is paid for.

No behavior change. 80 ai-vterm tests, 15 vterm-toggle tests, 15 cj-window-geometry tests all pass. Full make test green.

1 files changed, 4 insertions, 9 deletions

diff --git a/tests/test-vterm-toggle--dispatch.el b/tests/test-vterm-toggle--dispatch.el
index d63b3d35..93c06467 100644
--- a/tests/test-vterm-toggle--dispatch.el
+++ b/tests/test-vterm-toggle--dispatch.el
@@ -13,14 +13,9 @@
 (require 'cl-lib)
 
 (add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(add-to-list 'load-path (expand-file-name "tests" user-emacs-directory))
 (require 'eshell-vterm-config)
-
-(defun test-vterm-toggle--dispatch-cleanup ()
-  "Kill any leftover test buffers."
-  (dolist (b (buffer-list))
-    (let ((name (buffer-name b)))
-      (when (string-prefix-p "*test-vterm" name)
-        (kill-buffer b)))))
+(require 'testutil-vterm-buffers)
 
 (ert-deftest test-vterm-toggle--dispatch-window-displayed-returns-toggle-off ()
   "Normal: displayed vterm window -> (toggle-off . WIN)."
@@ -32,7 +27,7 @@
 
 (ert-deftest test-vterm-toggle--dispatch-no-window-buffer-alive-returns-show-recent ()
   "Normal: no displayed vterm, at least one alive -> show-recent + first."
-  (test-vterm-toggle--dispatch-cleanup)
+  (cj/test--kill-test-vterm-buffers)
   (let ((b1 (get-buffer-create "*test-vterm-mru-1*"))
         (b2 (get-buffer-create "*test-vterm-mru-2*")))
     (unwind-protect
@@ -47,7 +42,7 @@
 
 (ert-deftest test-vterm-toggle--dispatch-no-window-no-buffer-returns-create-new ()
   "Boundary: nothing displayed, no alive vterms -> create-new."
-  (test-vterm-toggle--dispatch-cleanup)
+  (cj/test--kill-test-vterm-buffers)
   (cl-letf (((symbol-function 'cj/--vterm-toggle-displayed-window)
              (lambda (&optional _frame) nil))
             ((symbol-function 'cj/--vterm-toggle-buffers)