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, 141 insertions, 0 deletions

diff --git a/tests/test-gptel-tools-write-text-file.el b/tests/test-gptel-tools-write-text-file.el
new file mode 100644
index 00000000..258ae8cc
--- /dev/null
+++ b/tests/test-gptel-tools-write-text-file.el
@@ -0,0 +1,141 @@
+;;; test-gptel-tools-write-text-file.el --- Tests for write_text_file gptel tool -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for `cj/write-text-file--run' and its helpers.
+
+;;; 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 'write_text_file)
+
+;; ------------------------------------------------------- helpers
+
+(defun test-gptel-tools-write-text-file--in-home (suffix fn)
+  "Run FN with a fresh path under HOME using SUFFIX.  Clean up after."
+  (let* ((name (format ".test-gptel-tools-write-text-file-%s-%s.tmp"
+                       suffix (format-time-string "%s%N")))
+         (path (expand-file-name name "~")))
+    (unwind-protect
+        (funcall fn path)
+      (when (file-exists-p path) (delete-file path))
+      (dolist (b (file-expand-wildcards (concat path "-*.bak")))
+        (when (file-exists-p b) (delete-file b))))))
+
+;; --------------------------------------------- validate-path
+
+(ert-deftest test-gptel-tools-write-text-file-validate-path-normal ()
+  "Normal: returns the expanded path for a HOME-relative input."
+  (let ((result (cj/write-text-file--validate-path "foo.txt")))
+    (should (string-prefix-p (expand-file-name "~") result))
+    (should (string-suffix-p "/foo.txt" result))))
+
+(ert-deftest test-gptel-tools-write-text-file-validate-path-error-outside-home ()
+  "Error: a path outside HOME signals."
+  (should-error (cj/write-text-file--validate-path "/etc/hostname")))
+
+;; --------------------------------------------- backup-name
+
+(ert-deftest test-gptel-tools-write-text-file-backup-name-shape ()
+  "Backup names append a YYYY-MM-DD-HHMMSS suffix and .bak."
+  (let ((name (cj/write-text-file--backup-name "/home/user/foo.txt")))
+    (should (string-prefix-p "/home/user/foo.txt-" name))
+    (should (string-suffix-p ".bak" name))
+    (should (string-match-p "-[0-9]\\{4\\}-[0-9]\\{2\\}-[0-9]\\{2\\}-[0-9]\\{6\\}\\.bak\\'"
+                            name))))
+
+;; --------------------------------------------- ensure-parent
+
+(ert-deftest test-gptel-tools-write-text-file-ensure-parent-creates-missing ()
+  "Normal: creates missing parent directories."
+  (let* ((base (make-temp-file "test-gptel-tools-write-text-file-" t))
+         (deep (expand-file-name "a/b/c/file.txt" base)))
+    (unwind-protect
+        (progn
+          (cj/write-text-file--ensure-parent deep)
+          (should (file-directory-p (file-name-directory deep))))
+      (delete-directory base t))))
+
+(ert-deftest test-gptel-tools-write-text-file-ensure-parent-error-unwritable ()
+  "Error: an unwritable parent signals."
+  (let* ((parent (make-temp-file "test-gptel-tools-write-text-file-ro-" t))
+         (target (expand-file-name "child.txt" parent)))
+    (unwind-protect
+        (progn
+          (set-file-modes parent #o500)
+          (should-error (cj/write-text-file--ensure-parent target)))
+      (set-file-modes parent #o700)
+      (delete-directory parent t))))
+
+;; --------------------------------------------- run
+
+(ert-deftest test-gptel-tools-write-text-file-run-normal ()
+  "Normal: writes new content and returns a status string."
+  (test-gptel-tools-write-text-file--in-home
+   "new"
+   (lambda (path)
+     (let ((result (cj/write-text-file--run
+                    (file-name-nondirectory path) "hello\n" nil)))
+       (should (string-match-p "Successfully wrote" result))
+       (with-temp-buffer
+         (insert-file-contents path)
+         (should (equal (buffer-string) "hello\n")))))))
+
+(ert-deftest test-gptel-tools-write-text-file-run-error-existing-no-overwrite ()
+  "Error: existing file without overwrite signals."
+  (test-gptel-tools-write-text-file--in-home
+   "existing"
+   (lambda (path)
+     (with-temp-file path (insert "old content\n"))
+     (should-error (cj/write-text-file--run
+                    (file-name-nondirectory path) "new content\n" nil))
+     ;; File preserved
+     (with-temp-buffer
+       (insert-file-contents path)
+       (should (equal (buffer-string) "old content\n"))))))
+
+(ert-deftest test-gptel-tools-write-text-file-run-overwrite-creates-backup ()
+  "Overwrite path makes a timestamped backup before writing."
+  (test-gptel-tools-write-text-file--in-home
+   "overwrite"
+   (lambda (path)
+     (with-temp-file path (insert "old content\n"))
+     (cj/write-text-file--run
+      (file-name-nondirectory path) "new content\n" t)
+     ;; New content landed
+     (with-temp-buffer
+       (insert-file-contents path)
+       (should (equal (buffer-string) "new content\n")))
+     ;; Backup exists with old content
+     (let ((backups (file-expand-wildcards (concat path "-*.bak"))))
+       (should (= 1 (length backups)))
+       (with-temp-buffer
+         (insert-file-contents (car backups))
+         (should (equal (buffer-string) "old content\n")))))))
+
+(ert-deftest test-gptel-tools-write-text-file-run-boundary-empty-content ()
+  "Boundary: nil content writes an empty file."
+  (test-gptel-tools-write-text-file--in-home
+   "empty"
+   (lambda (path)
+     (cj/write-text-file--run (file-name-nondirectory path) nil nil)
+     (should (file-exists-p path))
+     (should (= 0 (file-attribute-size (file-attributes path)))))))
+
+(ert-deftest test-gptel-tools-write-text-file-run-error-outside-home ()
+  "Error: a path outside HOME signals."
+  (should-error (cj/write-text-file--run "/etc/test-write.txt" "x" nil)))
+
+(provide 'test-gptel-tools-write-text-file)
+;;; test-gptel-tools-write-text-file.el ends here