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diff --git a/tests/test-modeline-config-buffer-status.el b/tests/test-modeline-config-buffer-status.el
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+++ b/tests/test-modeline-config-buffer-status.el
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+;;; test-modeline-config-buffer-status.el --- buffer-status segment -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for `cj/--modeline-buffer-status': the modified / read-only
+;; indicator.  Read-only wins over modified; the modified dot shows only
+;; for file-visiting buffers (special buffers are perpetually modified
+;; and would be noise); clean file buffers show nothing.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+(require 'modeline-config)
+
+(ert-deftest test-modeline-config-buffer-status-modified-file-shows-dot ()
+  "Normal: a modified file-visiting buffer returns the warning-faced dot."
+  (let ((file (make-temp-file "modeline-status-" nil ".txt")))
+    (unwind-protect
+        (with-current-buffer (find-file-noselect file)
+          (insert "x")
+          (let ((status (cj/--modeline-buffer-status)))
+            (should (stringp status))
+            (should (string-match-p "●" status))
+            (should (eq (get-text-property
+                         (string-match "●" status) 'face status)
+                        'warning)))
+          (set-buffer-modified-p nil)
+          (kill-buffer))
+      (delete-file file))))
+
+(ert-deftest test-modeline-config-buffer-status-clean-file-nil ()
+  "Normal: an unmodified file-visiting buffer returns nil."
+  (let ((file (make-temp-file "modeline-status-" nil ".txt")))
+    (unwind-protect
+        (with-current-buffer (find-file-noselect file)
+          (should-not (cj/--modeline-buffer-status))
+          (kill-buffer))
+      (delete-file file))))
+
+(ert-deftest test-modeline-config-buffer-status-read-only-shows-lock ()
+  "Normal: a read-only buffer returns the read-only indicator."
+  (with-temp-buffer
+    (setq buffer-read-only t)
+    (let ((status (cj/--modeline-buffer-status)))
+      (should (stringp status))
+      (should (> (length status) 0)))))
+
+(ert-deftest test-modeline-config-buffer-status-read-only-wins-over-modified ()
+  "Boundary: read-only + modified shows the read-only indicator, not the dot."
+  (let ((file (make-temp-file "modeline-status-" nil ".txt")))
+    (unwind-protect
+        (with-current-buffer (find-file-noselect file)
+          (insert "x")
+          (setq buffer-read-only t)
+          (let ((status (cj/--modeline-buffer-status)))
+            (should (stringp status))
+            (should-not (string-match-p "●" status)))
+          (setq buffer-read-only nil)
+          (set-buffer-modified-p nil)
+          (kill-buffer))
+      (delete-file file))))
+
+(ert-deftest test-modeline-config-buffer-status-modified-non-file-nil ()
+  "Boundary: a modified non-file buffer (scratch-like) returns nil."
+  (with-temp-buffer
+    (insert "x")
+    (should (buffer-modified-p))
+    (should-not (cj/--modeline-buffer-status))))
+
+(provide 'test-modeline-config-buffer-status)
+;;; test-modeline-config-buffer-status.el ends here