test+fix:custom-file-buffer: add tests, fix linter warning

  Add 58 unit tests for buffer/file utility functions:
  - cj/copy-link-to-buffer-file (12 tests)
  - cj/copy-path-to-buffer-file-as-kill (12 tests)
  - cj/copy-whole-buffer (14 tests)
  - cj/clear-to-bottom-of-buffer (10 tests)
  - cj/clear-to-top-of-buffer (10 tests)

  Tests cover normal cases, boundary cases (unicode, empty buffers, narrowing,
  read-only buffers), and error cases.

  Production code change:
  - Fix linter warning: unused variable 'err' → '_' in cj/move-buffer-and-file

1 files changed, 194 insertions, 0 deletions

diff --git a/tests/test-custom-file-buffer-copy-whole-buffer.el b/tests/test-custom-file-buffer-copy-whole-buffer.el
new file mode 100644
index 00000000..a0546b18
--- /dev/null
+++ b/tests/test-custom-file-buffer-copy-whole-buffer.el
@@ -0,0 +1,194 @@
+;;; test-custom-file-buffer-copy-whole-buffer.el --- Tests for cj/copy-whole-buffer -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the cj/copy-whole-buffer function from custom-file-buffer.el
+;;
+;; This function copies the entire contents of the current buffer to the kill ring.
+;; Point and mark are left exactly where they were. No transient region is created.
+
+;;; 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.")
+
+;; Stub ps-print package
+(provide 'ps-print)
+
+;; Now load the actual production module
+(require 'custom-file-buffer)
+
+;;; Setup and Teardown
+
+(defun test-copy-whole-buffer-setup ()
+  "Set up test environment."
+  (setq kill-ring nil))
+
+(defun test-copy-whole-buffer-teardown ()
+  "Clean up test environment."
+  (setq kill-ring nil))
+
+;;; Normal Cases
+
+(ert-deftest test-copy-whole-buffer-simple-text ()
+  "Should copy simple text content to kill ring."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "Hello, world!")
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "Hello, world!")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-preserves-point ()
+  "Should preserve point position."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "Hello, world!")
+        (goto-char 7)  ; Position in middle
+        (cj/copy-whole-buffer)
+        (should (= (point) 7)))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-preserves-mark ()
+  "Should preserve mark position."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "Hello, world!")
+        (push-mark 5)
+        (goto-char 10)
+        (cj/copy-whole-buffer)
+        (should (= (mark) 5))
+        (should (= (point) 10)))
+    (test-copy-whole-buffer-teardown)))
+
+;;; Boundary Cases
+
+(ert-deftest test-copy-whole-buffer-empty ()
+  "Should handle empty buffer."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-large ()
+  "Should handle very large buffer."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (let ((large-content (make-string 100000 ?x)))
+          (insert large-content)
+          (cj/copy-whole-buffer)
+          (should (equal (car kill-ring) large-content))))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-unicode ()
+  "Should handle unicode content (emoji, RTL text)."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "Hello 👋 مرحبا")
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "Hello 👋 مرحبا")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-binary ()
+  "Should handle binary content."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert (string 0 1 2 255))
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) (string 0 1 2 255))))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-only-whitespace ()
+  "Should handle buffer with only whitespace."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "   \t\n  ")
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "   \t\n  ")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-newlines-at-boundaries ()
+  "Should handle newlines at start/end."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "\n\nHello\n\n")
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "\n\nHello\n\n")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-narrowed ()
+  "Should copy only visible region in narrowed buffer."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "Line 1\nLine 2\nLine 3\n")
+        (goto-char (point-min))
+        (forward-line 1)
+        (narrow-to-region (point) (progn (forward-line 1) (point)))
+        (cj/copy-whole-buffer)
+        ;; Should copy only the narrowed region
+        (should (equal (car kill-ring) "Line 2\n")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-read-only ()
+  "Should work in read-only buffer."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "Read-only content")
+        (read-only-mode 1)
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "Read-only content")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-kill-ring-has-content ()
+  "Should add to kill ring when it already has content."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "New content")
+        (kill-new "existing content")
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "New content"))
+        (should (equal (cadr kill-ring) "existing content")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-multiline ()
+  "Should preserve multiline content."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert "Line 1\nLine 2\nLine 3")
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "Line 1\nLine 2\nLine 3")))
+    (test-copy-whole-buffer-teardown)))
+
+(ert-deftest test-copy-whole-buffer-no-properties ()
+  "Should strip text properties."
+  (test-copy-whole-buffer-setup)
+  (unwind-protect
+      (with-temp-buffer
+        (insert (propertize "Hello" 'face 'bold))
+        (cj/copy-whole-buffer)
+        (should (equal (car kill-ring) "Hello"))
+        (should (null (text-properties-at 0 (car kill-ring)))))
+    (test-copy-whole-buffer-teardown)))
+
+(provide 'test-custom-file-buffer-copy-whole-buffer)
+;;; test-custom-file-buffer-copy-whole-buffer.el ends here