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+;;; test-custom-misc-replace-fraction-glyphs.el --- Tests for cj/--replace-fraction-glyphs -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the cj/--replace-fraction-glyphs function from custom-misc.el
+;;
+;; This function bidirectionally converts between text fractions (1/4) and
+;; Unicode fraction glyphs (¼). It supports 5 common fractions:
+;; - 1/4 ↔ ¼
+;; - 1/2 ↔ ½
+;; - 3/4 ↔ ¾
+;; - 1/3 ↔ ⅓
+;; - 2/3 ↔ ⅔
+;;
+;; We test the NON-INTERACTIVE implementation (cj/--replace-fraction-glyphs)
+;; to avoid mocking prefix arguments. This follows our testing best practice
+;; of separating business logic from UI interaction.
+
+;;; Code:
+
+(require 'ert)
+(require 'testutil-general)
+
+;; Add modules directory to load path
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+;; Stub dependencies before loading the module
+(defvar cj/custom-keymap (make-sparse-keymap)
+  "Stub keymap for testing.")
+
+;; Now load the actual production module
+(require 'custom-misc)
+
+;;; Test Helpers
+
+(defun test-replace-fraction-glyphs (input-text to-glyphs)
+  "Test cj/--replace-fraction-glyphs on INPUT-TEXT.
+TO-GLYPHS determines conversion direction.
+Returns the buffer string after operation."
+  (with-temp-buffer
+    (insert input-text)
+    (cj/--replace-fraction-glyphs (point-min) (point-max) to-glyphs)
+    (buffer-string)))
+
+;;; Normal Cases - Text to Glyphs
+
+(ert-deftest test-replace-fraction-glyphs-text-to-glyph-quarter ()
+  "Should convert 1/4 to ¼."
+  (let ((result (test-replace-fraction-glyphs "1/4" t)))
+    (should (string= result "¼"))))
+
+(ert-deftest test-replace-fraction-glyphs-text-to-glyph-half ()
+  "Should convert 1/2 to ½."
+  (let ((result (test-replace-fraction-glyphs "1/2" t)))
+    (should (string= result "½"))))
+
+(ert-deftest test-replace-fraction-glyphs-text-to-glyph-three-quarters ()
+  "Should convert 3/4 to ¾."
+  (let ((result (test-replace-fraction-glyphs "3/4" t)))
+    (should (string= result "¾"))))
+
+(ert-deftest test-replace-fraction-glyphs-text-to-glyph-third ()
+  "Should convert 1/3 to ⅓."
+  (let ((result (test-replace-fraction-glyphs "1/3" t)))
+    (should (string= result "⅓"))))
+
+(ert-deftest test-replace-fraction-glyphs-text-to-glyph-two-thirds ()
+  "Should convert 2/3 to ⅔."
+  (let ((result (test-replace-fraction-glyphs "2/3" t)))
+    (should (string= result "⅔"))))
+
+(ert-deftest test-replace-fraction-glyphs-text-to-glyph-multiple ()
+  "Should convert multiple fractions in text."
+  (let ((result (test-replace-fraction-glyphs "Use 1/4 cup and 1/2 teaspoon" t)))
+    (should (string= result "Use ¼ cup and ½ teaspoon"))))
+
+(ert-deftest test-replace-fraction-glyphs-text-to-glyph-all-types ()
+  "Should convert all fraction types."
+  (let ((result (test-replace-fraction-glyphs "1/4 1/2 3/4 1/3 2/3" t)))
+    (should (string= result "¼ ½ ¾ ⅓ ⅔"))))
+
+;;; Normal Cases - Glyphs to Text
+
+(ert-deftest test-replace-fraction-glyphs-glyph-to-text-quarter ()
+  "Should convert ¼ to 1/4."
+  (let ((result (test-replace-fraction-glyphs "¼" nil)))
+    (should (string= result "1/4"))))
+
+(ert-deftest test-replace-fraction-glyphs-glyph-to-text-half ()
+  "Should convert ½ to 1/2."
+  (let ((result (test-replace-fraction-glyphs "½" nil)))
+    (should (string= result "1/2"))))
+
+(ert-deftest test-replace-fraction-glyphs-glyph-to-text-three-quarters ()
+  "Should convert ¾ to 3/4."
+  (let ((result (test-replace-fraction-glyphs "¾" nil)))
+    (should (string= result "3/4"))))
+
+(ert-deftest test-replace-fraction-glyphs-glyph-to-text-third ()
+  "Should convert ⅓ to 1/3."
+  (let ((result (test-replace-fraction-glyphs "⅓" nil)))
+    (should (string= result "1/3"))))
+
+(ert-deftest test-replace-fraction-glyphs-glyph-to-text-two-thirds ()
+  "Should convert ⅔ to 2/3."
+  (let ((result (test-replace-fraction-glyphs "⅔" nil)))
+    (should (string= result "2/3"))))
+
+(ert-deftest test-replace-fraction-glyphs-glyph-to-text-multiple ()
+  "Should convert multiple glyphs in text."
+  (let ((result (test-replace-fraction-glyphs "Use ¼ cup and ½ teaspoon" nil)))
+    (should (string= result "Use 1/4 cup and 1/2 teaspoon"))))
+
+(ert-deftest test-replace-fraction-glyphs-glyph-to-text-all-types ()
+  "Should convert all glyph types."
+  (let ((result (test-replace-fraction-glyphs "¼ ½ ¾ ⅓ ⅔" nil)))
+    (should (string= result "1/4 1/2 3/4 1/3 2/3"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-replace-fraction-glyphs-empty-string ()
+  "Should handle empty string."
+  (let ((result (test-replace-fraction-glyphs "" t)))
+    (should (string= result ""))))
+
+(ert-deftest test-replace-fraction-glyphs-no-fractions-to-glyphs ()
+  "Should handle text with no fractions (no-op) when converting to glyphs."
+  (let ((result (test-replace-fraction-glyphs "hello world" t)))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-replace-fraction-glyphs-no-fractions-to-text ()
+  "Should handle text with no glyphs (no-op) when converting to text."
+  (let ((result (test-replace-fraction-glyphs "hello world" nil)))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-replace-fraction-glyphs-at-start ()
+  "Should handle fraction at start of text."
+  (let ((result (test-replace-fraction-glyphs "1/2 of the total" t)))
+    (should (string= result "½ of the total"))))
+
+(ert-deftest test-replace-fraction-glyphs-at-end ()
+  "Should handle fraction at end of text."
+  (let ((result (test-replace-fraction-glyphs "Reduce by 1/4" t)))
+    (should (string= result "Reduce by ¼"))))
+
+(ert-deftest test-replace-fraction-glyphs-repeated ()
+  "Should handle repeated fractions."
+  (let ((result (test-replace-fraction-glyphs "1/4 and 1/4 and 1/4" t)))
+    (should (string= result "¼ and ¼ and ¼"))))
+
+(ert-deftest test-replace-fraction-glyphs-very-long-text ()
+  "Should handle very long text with many fractions."
+  (let* ((long-text (mapconcat (lambda (_) "1/4") (make-list 50 nil) " "))
+         (result (test-replace-fraction-glyphs long-text t)))
+    (should (string-match-p "¼" result))
+    (should-not (string-match-p "1/4" result))))
+
+(ert-deftest test-replace-fraction-glyphs-bidirectional ()
+  "Should correctly convert back and forth."
+  (let* ((original "Use 1/4 cup")
+         (to-glyph (test-replace-fraction-glyphs original t))
+         (back-to-text (test-replace-fraction-glyphs to-glyph nil)))
+    (should (string= to-glyph "Use ¼ cup"))
+    (should (string= back-to-text original))))
+
+;;; Error Cases
+
+(ert-deftest test-replace-fraction-glyphs-start-greater-than-end ()
+  "Should error when start > end."
+  (should-error
+   (with-temp-buffer
+     (insert "1/4")
+     (cj/--replace-fraction-glyphs (point-max) (point-min) t))
+   :type 'error))
+
+(ert-deftest test-replace-fraction-glyphs-empty-region ()
+  "Should handle empty region (start == end) without error."
+  (with-temp-buffer
+    (insert "1/4")
+    (let ((pos (/ (+ (point-min) (point-max)) 2)))
+      (cj/--replace-fraction-glyphs pos pos t)
+      ;; Should complete without error
+      (should (string= (buffer-string) "1/4")))))
+
+(provide 'test-custom-misc-replace-fraction-glyphs)
+;;; test-custom-misc-replace-fraction-glyphs.el ends here