test(gptel-tools): cover the helpers across the five remaining tools

The gptel-tools files had zero direct coverage outside of
`update_text_file`, which landed with its rewrite earlier this
session.  This commit adds 52 tests across the five other tools.

For three of the tools the helpers were already top-level defuns
(`read_text_file`, `list_directory_files`, `move_to_trash`).  The
other two had their main bodies inlined into the `gptel-make-tool`
lambda -- I extracted them so the work is testable without mocking
gptel itself:

  read_buffer.el     -> `cj/read-buffer--get-content`
  write_text_file.el -> `cj/write-text-file--run` plus
                        `--validate-path`, `--backup-name`,
                        `--ensure-parent`

Test files, by tool:

- read_buffer.el          (5 tests):  normal, empty, buffer-object,
  text-property-stripping, missing buffer.
- write_text_file.el     (10 tests):  validate-path, backup-name
  shape, ensure-parent (creates missing / rejects unwritable), run
  with normal / overwrite / existing-no-overwrite / empty content /
  outside-home.
- read_text_file.el      (12 tests):  validate-file-path (normal +
  three error shapes), metadata plist shape, size limits (no-op /
  hard cap / warning bypass with no-confirm), binary detection
  (text vs null-byte), special-type EPUB and generic-binary paths.
- list_directory_files.el (15 tests):  mode-to-permissions (file /
  dir / executable), get-file-info (file / directory), extension
  filter (keep / drop / always-dir / nil-extension), format-file-
  entry, list-directory flat / recursive / error, format-output
  with and without files.
- move_to_trash.el       (10 tests):  unique-name (no conflict /
  conflict with timestamp / no-extension), validate-path (HOME / /tmp
  / outside / critical-dir / missing), perform on file and
  directory.

Each test file uses the same load-path / gptel-stub idiom
(`eval-and-compile` block, gptel stub when the real package isn't
available) so the byte-compile hook is happy.

1 files changed, 60 insertions, 0 deletions

diff --git a/tests/test-gptel-tools-read-buffer.el b/tests/test-gptel-tools-read-buffer.el
new file mode 100644
index 00000000..75efd604
--- /dev/null
+++ b/tests/test-gptel-tools-read-buffer.el
@@ -0,0 +1,60 @@
+;;; test-gptel-tools-read-buffer.el --- Tests for read_buffer gptel tool -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for `cj/read-buffer--get-content', the testable helper that
+;; backs the read_buffer gptel tool.
+
+;;; Code:
+
+(require 'ert)
+
+(eval-and-compile
+  (add-to-list 'load-path (expand-file-name "tests" user-emacs-directory))
+  (add-to-list 'load-path (expand-file-name "gptel-tools" user-emacs-directory))
+  (setq load-prefer-newer t)
+  (unless (featurep 'gptel)
+    (defvar gptel-tools nil)
+    (defun gptel-make-tool (&rest _args) nil)
+    (defun gptel-get-tool (&rest _args) nil)
+    (provide 'gptel)))
+
+(require 'read_buffer)
+
+(ert-deftest test-gptel-tools-read-buffer-normal ()
+  "Normal: returns the contents of an existing buffer."
+  (with-temp-buffer
+    (rename-buffer "test-gptel-tools-read-buffer-normal" t)
+    (insert "hello world")
+    (should (equal (cj/read-buffer--get-content (buffer-name)) "hello world"))))
+
+(ert-deftest test-gptel-tools-read-buffer-boundary-empty-buffer ()
+  "Boundary: empty buffer returns the empty string."
+  (with-temp-buffer
+    (rename-buffer "test-gptel-tools-read-buffer-empty" t)
+    (should (equal (cj/read-buffer--get-content (buffer-name)) ""))))
+
+(ert-deftest test-gptel-tools-read-buffer-boundary-buffer-object ()
+  "Boundary: accepts a buffer object as well as a name string."
+  (with-temp-buffer
+    (insert "from buffer object")
+    (should (equal (cj/read-buffer--get-content (current-buffer))
+                   "from buffer object"))))
+
+(ert-deftest test-gptel-tools-read-buffer-boundary-strips-text-properties ()
+  "Boundary: the returned string has no text properties."
+  (with-temp-buffer
+    (rename-buffer "test-gptel-tools-read-buffer-props" t)
+    (insert (propertize "fontified" 'face 'bold))
+    (let ((content (cj/read-buffer--get-content (buffer-name))))
+      (should (equal content "fontified"))
+      (should-not (text-properties-at 0 content)))))
+
+(ert-deftest test-gptel-tools-read-buffer-error-missing-buffer ()
+  "Error: nonexistent buffer name signals."
+  (when (get-buffer "test-gptel-tools-read-buffer-absent")
+    (kill-buffer "test-gptel-tools-read-buffer-absent"))
+  (should-error (cj/read-buffer--get-content
+                 "test-gptel-tools-read-buffer-absent")))
+
+(provide 'test-gptel-tools-read-buffer)
+;;; test-gptel-tools-read-buffer.el ends here