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diff --git a/tests/test-ai-vterm--window-geometry.el b/tests/test-ai-vterm--window-geometry.el
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+;;; test-ai-vterm--window-geometry.el --- Tests for direction + fraction helpers -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Two pure helpers used by F9's geometry-preservation feature:
+;;
+;; - `cj/--ai-vterm-window-direction' classifies a window's position
+;;   relative to its frame as right / below / left / above (with a
+;;   right fallback when the window fills the frame).
+;;
+;; - `cj/--ai-vterm-window-fraction' returns the window's size on
+;;   the matching axis as a fraction of the frame.
+;;
+;; Tests use real window splits in `save-window-excursion' rather
+;; than mocking, since the helpers consume `window-edges' and
+;; `frame-width' / `frame-height' directly.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'ai-vterm)
+
+(ert-deftest test-ai-vterm--window-direction-right-split ()
+  "Normal: 2-window vertical split, right-side window -> right."
+  (save-window-excursion
+    (delete-other-windows)
+    (let ((right (split-window (selected-window) nil 'right)))
+      (should (eq (cj/--ai-vterm-window-direction right) 'right)))))
+
+(ert-deftest test-ai-vterm--window-direction-left-split ()
+  "Normal: 2-window vertical split, left-side window -> left."
+  (save-window-excursion
+    (delete-other-windows)
+    (split-window (selected-window) nil 'right)
+    (should (eq (cj/--ai-vterm-window-direction (selected-window)) 'left))))
+
+(ert-deftest test-ai-vterm--window-direction-below-split ()
+  "Normal: 2-window horizontal split, bottom window -> below."
+  (save-window-excursion
+    (delete-other-windows)
+    (let ((below (split-window (selected-window) nil 'below)))
+      (should (eq (cj/--ai-vterm-window-direction below) 'below)))))
+
+(ert-deftest test-ai-vterm--window-direction-above-split ()
+  "Normal: 2-window horizontal split, top window -> above."
+  (save-window-excursion
+    (delete-other-windows)
+    (split-window (selected-window) nil 'below)
+    (should (eq (cj/--ai-vterm-window-direction (selected-window)) 'above))))
+
+(ert-deftest test-ai-vterm--window-direction-single-window-fallback ()
+  "Boundary: single-window frame -> default right."
+  (save-window-excursion
+    (delete-other-windows)
+    (should (eq (cj/--ai-vterm-window-direction (selected-window)) 'right))))
+
+(ert-deftest test-ai-vterm--window-fraction-right-split-half ()
+  "Normal: right window of equal vertical split -> ~0.5 width fraction."
+  (save-window-excursion
+    (delete-other-windows)
+    (let* ((right (split-window (selected-window) nil 'right))
+           (frac (cj/--ai-vterm-window-fraction right 'right)))
+      (should (and (> frac 0.4) (< frac 0.6))))))
+
+(ert-deftest test-ai-vterm--window-fraction-below-split-half ()
+  "Normal: bottom window of equal horizontal split -> ~0.5 height fraction."
+  (save-window-excursion
+    (delete-other-windows)
+    (let* ((below (split-window (selected-window) nil 'below))
+           (frac (cj/--ai-vterm-window-fraction below 'below)))
+      (should (and (> frac 0.4) (< frac 0.6))))))
+
+(ert-deftest test-ai-vterm--window-fraction-narrow-right-split ()
+  "Normal: right window at 1/4 width -> fraction within that range."
+  (save-window-excursion
+    (delete-other-windows)
+    (let* ((frame-w (frame-width))
+           (target-cols (/ frame-w 4))
+           (right (split-window (selected-window) (- target-cols) 'right))
+           (frac (cj/--ai-vterm-window-fraction right 'right)))
+      (should (and (> frac 0.15) (< frac 0.35))))))
+
+(provide 'test-ai-vterm--window-geometry)
+;;; test-ai-vterm--window-geometry.el ends here