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diff --git a/tests/test-nov-reading--text-scale.el b/tests/test-nov-reading--text-scale.el
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+;;; test-nov-reading--text-scale.el --- nov reading text-scale persistence tests -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the persisted global reading text-scale offset: parsing the stored
+;; value (pure) and the save/load round-trip through the data file.  The live
+;; text-scale application in the +/-/= commands is exercised live, not here.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'nov-reading)
+
+(declare-function cj/nov-reading--parse-text-scale "nov-reading" (s))
+(declare-function cj/nov-reading--load-text-scale "nov-reading" ())
+(declare-function cj/nov-reading--save-text-scale "nov-reading" (amount))
+(defvar cj/nov-reading-text-scale-file)
+
+;;; --------------------- cj/nov-reading--parse-text-scale ----------------------
+
+(ert-deftest test-nov-reading-parse-text-scale-positive ()
+  "Normal: a positive integer string parses to that integer."
+  (should (= (cj/nov-reading--parse-text-scale "3") 3)))
+
+(ert-deftest test-nov-reading-parse-text-scale-negative ()
+  "Normal: a negative integer string parses to that integer."
+  (should (= (cj/nov-reading--parse-text-scale "-2") -2)))
+
+(ert-deftest test-nov-reading-parse-text-scale-trailing-newline ()
+  "Boundary: surrounding whitespace/newline is tolerated."
+  (should (= (cj/nov-reading--parse-text-scale "4\n") 4)))
+
+(ert-deftest test-nov-reading-parse-text-scale-zero ()
+  "Boundary: \"0\" parses to 0."
+  (should (= (cj/nov-reading--parse-text-scale "0") 0)))
+
+(ert-deftest test-nov-reading-parse-text-scale-nil ()
+  "Boundary: nil parses to 0."
+  (should (= (cj/nov-reading--parse-text-scale nil) 0)))
+
+(ert-deftest test-nov-reading-parse-text-scale-empty ()
+  "Boundary: an empty string parses to 0."
+  (should (= (cj/nov-reading--parse-text-scale "") 0)))
+
+(ert-deftest test-nov-reading-parse-text-scale-garbage ()
+  "Error: non-numeric content parses to 0."
+  (should (= (cj/nov-reading--parse-text-scale "garbage") 0)))
+
+(ert-deftest test-nov-reading-parse-text-scale-float-rejected ()
+  "Error: a non-integer numeric string parses to 0 (offsets are integers)."
+  (should (= (cj/nov-reading--parse-text-scale "3.5") 0)))
+
+;;; ------------------ cj/nov-reading--save/load round-trip ---------------------
+
+(ert-deftest test-nov-reading-save-load-roundtrip-positive ()
+  "Normal: a saved positive offset loads back unchanged."
+  (let ((cj/nov-reading-text-scale-file (make-temp-file "nov-scale-")))
+    (unwind-protect
+        (progn
+          (cj/nov-reading--save-text-scale 4)
+          (should (= (cj/nov-reading--load-text-scale) 4)))
+      (delete-file cj/nov-reading-text-scale-file))))
+
+(ert-deftest test-nov-reading-save-load-roundtrip-negative ()
+  "Normal: a saved negative offset loads back unchanged."
+  (let ((cj/nov-reading-text-scale-file (make-temp-file "nov-scale-")))
+    (unwind-protect
+        (progn
+          (cj/nov-reading--save-text-scale -3)
+          (should (= (cj/nov-reading--load-text-scale) -3)))
+      (delete-file cj/nov-reading-text-scale-file))))
+
+(ert-deftest test-nov-reading-save-load-roundtrip-zero ()
+  "Boundary: a saved 0 offset loads back as 0."
+  (let ((cj/nov-reading-text-scale-file (make-temp-file "nov-scale-")))
+    (unwind-protect
+        (progn
+          (cj/nov-reading--save-text-scale 0)
+          (should (= (cj/nov-reading--load-text-scale) 0)))
+      (delete-file cj/nov-reading-text-scale-file))))
+
+(ert-deftest test-nov-reading-load-missing-file-defaults-zero ()
+  "Boundary: loading when no file exists yet returns 0."
+  (let ((cj/nov-reading-text-scale-file
+         (expand-file-name "nov-scale-absent"
+                           (make-temp-file "nov-scale-dir-" t))))
+    (unwind-protect
+        (should (= (cj/nov-reading--load-text-scale) 0))
+      (delete-directory (file-name-directory cj/nov-reading-text-scale-file) t))))
+
+(ert-deftest test-nov-reading-save-creates-missing-directory ()
+  "Boundary: save creates the data directory when it is absent."
+  (let* ((dir (make-temp-file "nov-scale-dir-" t))
+         (cj/nov-reading-text-scale-file
+          (expand-file-name "sub/nov-reading-text-scale" dir)))
+    (unwind-protect
+        (progn
+          (cj/nov-reading--save-text-scale 2)
+          (should (file-readable-p cj/nov-reading-text-scale-file))
+          (should (= (cj/nov-reading--load-text-scale) 2)))
+      (delete-directory dir t))))
+
+(provide 'test-nov-reading--text-scale)
+;;; test-nov-reading--text-scale.el ends here