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, 117 insertions, 0 deletions

diff --git a/tests/test-gptel-tools-read-text-file.el b/tests/test-gptel-tools-read-text-file.el
new file mode 100644
index 000000000..3a4f6662d
--- /dev/null
+++ b/tests/test-gptel-tools-read-text-file.el
@@ -0,0 +1,117 @@
+;;; test-gptel-tools-read-text-file.el --- Tests for read_text_file gptel tool -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the helpers in read_text_file.el.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(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_text_file)
+
+;; -------------------------- helpers
+
+(defun test-gptel-tools-read-text-file--in-home (suffix content fn)
+  "Run FN with a temp file (containing CONTENT) under HOME using SUFFIX."
+  (let* ((name (format ".test-gptel-tools-read-text-file-%s-%s.tmp"
+                       suffix (format-time-string "%s%N")))
+         (path (expand-file-name name "~")))
+    (unwind-protect
+        (progn
+          (with-temp-file path (insert content))
+          (funcall fn path))
+      (when (file-exists-p path) (delete-file path)))))
+
+;; -------------------------- validate-file-path
+
+(ert-deftest test-gptel-tools-read-text-file-validate-path-normal ()
+  "Normal: an existing readable file under HOME passes."
+  (test-gptel-tools-read-text-file--in-home
+   "normal" "hi"
+   (lambda (path)
+     (should (equal (cj/validate-file-path path) (file-truename path))))))
+
+(ert-deftest test-gptel-tools-read-text-file-validate-path-error-outside-home ()
+  "Error: path outside HOME signals."
+  (should-error (cj/validate-file-path "/etc/hostname")))
+
+(ert-deftest test-gptel-tools-read-text-file-validate-path-error-missing ()
+  "Error: missing file signals."
+  (let ((path (expand-file-name
+               (format ".test-gptel-tools-read-text-file-missing-%s.tmp"
+                       (format-time-string "%s%N"))
+               "~")))
+    (when (file-exists-p path) (delete-file path))
+    (should-error (cj/validate-file-path path))))
+
+(ert-deftest test-gptel-tools-read-text-file-validate-path-error-directory ()
+  "Error: a directory signals."
+  (should-error (cj/validate-file-path "~")))
+
+;; -------------------------- get-file-metadata
+
+(ert-deftest test-gptel-tools-read-text-file-get-metadata-shape ()
+  "Returns a plist with :size and :string keys."
+  (test-gptel-tools-read-text-file--in-home
+   "meta" "abc"
+   (lambda (path)
+     (let ((meta (cj/get-file-metadata path)))
+       (should (plist-get meta :size))
+       (should (= 3 (plist-get meta :size)))
+       (should (stringp (plist-get meta :string)))
+       (should (string-match-p "modified" (plist-get meta :string)))))))
+
+;; -------------------------- check-file-size-limits
+
+(ert-deftest test-gptel-tools-read-text-file-size-limits-normal ()
+  "Small size below warning limit is a no-op."
+  (should-not (cj/check-file-size-limits 1024 nil)))
+
+(ert-deftest test-gptel-tools-read-text-file-size-limits-error-hard-cap ()
+  "Sizes above 100MB always signal."
+  (should-error (cj/check-file-size-limits (* 101 1024 1024) t))
+  (should-error (cj/check-file-size-limits (* 101 1024 1024) nil)))
+
+(ert-deftest test-gptel-tools-read-text-file-size-limits-warning-with-no-confirm ()
+  "Above 10MB but below 100MB with no-confirm passes through silently."
+  (should-not (cj/check-file-size-limits (* 11 1024 1024) t)))
+
+;; -------------------------- detect-binary-file
+
+(ert-deftest test-gptel-tools-read-text-file-detect-binary-text-file ()
+  "Text file: detect-binary returns nil."
+  (test-gptel-tools-read-text-file--in-home
+   "text" "plain ascii content"
+   (lambda (path)
+     (should-not (cj/detect-binary-file path)))))
+
+(ert-deftest test-gptel-tools-read-text-file-detect-binary-with-null-byte ()
+  "File with NUL in first 1024 bytes returns truthy."
+  (test-gptel-tools-read-text-file--in-home
+   "bin" (concat "head\0tail")
+   (lambda (path)
+     (should (cj/detect-binary-file path)))))
+
+;; -------------------------- handle-special-file-types
+
+(ert-deftest test-gptel-tools-read-text-file-handle-special-epub-error ()
+  "EPUB special-type handler signals \"not yet implemented\"."
+  (should-error (cj/handle-special-file-types "/tmp/foo.epub" t)))
+
+(ert-deftest test-gptel-tools-read-text-file-handle-special-binary-returns-nil ()
+  "Generic binary file with no-confirm returns nil to indicate normal read."
+  (should-not (cj/handle-special-file-types "/tmp/foo.bin" t)))
+
+(provide 'test-gptel-tools-read-text-file)
+;;; test-gptel-tools-read-text-file.el ends here