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+;;; test-custom-whitespace-remove-leading-trailing.el --- Tests for cj/--remove-leading-trailing-whitespace -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the cj/--remove-leading-trailing-whitespace function from custom-whitespace.el
+;;
+;; This function removes leading and trailing whitespace (spaces and tabs) from text.
+;; - Removes leading whitespace: ^[ \t]+
+;; - Removes trailing whitespace: [ \t]+$
+;; - Preserves interior whitespace
+;; - Operates on any region defined by START and END
+;;
+;; We test the NON-INTERACTIVE implementation (cj/--remove-leading-trailing-whitespace)
+;; to avoid mocking region selection and 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-whitespace)
+
+;;; Test Helpers
+
+(defun test-remove-leading-trailing (input-text)
+  "Test cj/--remove-leading-trailing-whitespace on INPUT-TEXT.
+Returns the buffer string after operation."
+  (with-temp-buffer
+    (insert input-text)
+    (cj/--remove-leading-trailing-whitespace (point-min) (point-max))
+    (buffer-string)))
+
+;;; Normal Cases
+
+(ert-deftest test-remove-leading-trailing-leading-spaces ()
+  "Should remove leading spaces from single line."
+  (let ((result (test-remove-leading-trailing "    hello world")))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-remove-leading-trailing-trailing-spaces ()
+  "Should remove trailing spaces from single line."
+  (let ((result (test-remove-leading-trailing "hello world    ")))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-remove-leading-trailing-both-spaces ()
+  "Should remove both leading and trailing spaces."
+  (let ((result (test-remove-leading-trailing "    hello world    ")))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-remove-leading-trailing-leading-tabs ()
+  "Should remove leading tabs from single line."
+  (let ((result (test-remove-leading-trailing "\t\thello world")))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-remove-leading-trailing-trailing-tabs ()
+  "Should remove trailing tabs from single line."
+  (let ((result (test-remove-leading-trailing "hello world\t\t")))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-remove-leading-trailing-mixed-tabs-spaces ()
+  "Should remove mixed tabs and spaces."
+  (let ((result (test-remove-leading-trailing " \t hello world \t ")))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-remove-leading-trailing-preserve-interior ()
+  "Should preserve interior whitespace."
+  (let ((result (test-remove-leading-trailing "  hello   world  \t")))
+    (should (string= result "hello   world"))))
+
+(ert-deftest test-remove-leading-trailing-multiple-lines ()
+  "Should handle multiple lines with leading/trailing whitespace."
+  (let ((result (test-remove-leading-trailing "  line1  \n\t\tline2\t\n   line3   ")))
+    (should (string= result "line1\nline2\nline3"))))
+
+(ert-deftest test-remove-leading-trailing-multiline-preserve-interior ()
+  "Should preserve interior whitespace on multiple lines."
+  (let ((result (test-remove-leading-trailing "  hello   world  \n  foo   bar  ")))
+    (should (string= result "hello   world\nfoo   bar"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-remove-leading-trailing-empty-string ()
+  "Should handle empty string."
+  (let ((result (test-remove-leading-trailing "")))
+    (should (string= result ""))))
+
+(ert-deftest test-remove-leading-trailing-single-char ()
+  "Should handle single character with surrounding spaces."
+  (let ((result (test-remove-leading-trailing "   x   ")))
+    (should (string= result "x"))))
+
+(ert-deftest test-remove-leading-trailing-only-whitespace ()
+  "Should handle lines with only whitespace."
+  (let ((result (test-remove-leading-trailing "   \t   ")))
+    (should (string= result ""))))
+
+(ert-deftest test-remove-leading-trailing-no-whitespace ()
+  "Should handle text with no leading/trailing whitespace (no-op)."
+  (let ((result (test-remove-leading-trailing "hello world")))
+    (should (string= result "hello world"))))
+
+(ert-deftest test-remove-leading-trailing-very-long-line ()
+  "Should handle very long lines with whitespace."
+  (let* ((long-text (make-string 500 ?x))
+         (input (concat "  " long-text "  "))
+         (result (test-remove-leading-trailing input)))
+    (should (string= result long-text))))
+
+(ert-deftest test-remove-leading-trailing-whitespace-between-lines ()
+  "Should handle lines that become empty after removal."
+  (let ((result (test-remove-leading-trailing "line1\n   \nline2")))
+    (should (string= result "line1\n\nline2"))))
+
+(ert-deftest test-remove-leading-trailing-newlines-only ()
+  "Should preserve newlines while removing spaces."
+  (let ((result (test-remove-leading-trailing "\n\n\n")))
+    (should (string= result "\n\n\n"))))
+
+(ert-deftest test-remove-leading-trailing-partial-region ()
+  "Should work on partial buffer region."
+  (with-temp-buffer
+    (insert "  hello  \n  world  \n  test  ")
+    ;; Only operate on middle line
+    (let ((start (+ (point-min) 10))  ; Start of second line
+          (end (+ (point-min) 19)))    ; End of second line
+      (cj/--remove-leading-trailing-whitespace start end)
+      (should (string= (buffer-string) "  hello  \nworld\n  test  ")))))
+
+;;; Error Cases
+
+(ert-deftest test-remove-leading-trailing-start-greater-than-end ()
+  "Should error when start > end."
+  (should-error
+   (with-temp-buffer
+     (insert "hello world")
+     (cj/--remove-leading-trailing-whitespace (point-max) (point-min)))
+   :type 'error))
+
+(ert-deftest test-remove-leading-trailing-empty-region ()
+  "Should handle empty region (start == end) without error."
+  (with-temp-buffer
+    (insert "hello world")
+    (let ((pos (/ (+ (point-min) (point-max)) 2)))
+      (cj/--remove-leading-trailing-whitespace pos pos)
+      ;; Should complete without error and not change buffer
+      (should (string= (buffer-string) "hello world")))))
+
+(provide 'test-custom-whitespace-remove-leading-trailing)
+;;; test-custom-whitespace-remove-leading-trailing.el ends here