Add c-ts-mode tests

* test/lisp/progmodes/c-ts-mode-resources/indent.erts: New .erts file
to test indentation of typical C constructs and prevent regression of
bug fixes.
* test/lisp/progmodes/c-ts-mode-tests.el: New file with c-ts-mode
tests.

test/lisp/progmodes/c-ts-mode-resources/indent.erts

@@ -0,0 +1,44 @@
+Code:
+  (lambda ()
+    (c-ts-mode)
+    (indent-region (point-min) (point-max)))
+
+Name: Basic
+
+=-=
+int
+main (void)
+{
+  return 0;
+}
+=-=-=
+
+Name: Hanging Braces (GNU Style)
+
+=-=
+int
+main (void)
+{
+  if (true)
+    {
+    }
+}
+=-=-=
+
+Name: Multiline Parameter List (bug#60398)
+
+=-=
+int f2(int x,
+       int y) {
+  return x + y;
+};
+=-=-=
+
+Name: Multiline Block Comments (bug#60270)
+
+=-=
+/**
+ * @some_func:
+ * @arg1:
+ */
+=-=-=

test/lisp/progmodes/c-ts-mode-tests.el

@@ -0,0 +1,31 @@
+;;; c-ts-mode-tests.el --- Tests for Tree-sitter-based C mode         -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2023 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ert)
+(require 'ert-x)
+(require 'treesit)
+
+(ert-deftest c-ts-mode-test-indentation ()
+  (skip-unless (treesit-ready-p 'c))
+  (ert-test-erts-file (ert-resource-file "indent.erts")))
+
+(provide 'c-ts-mode-tests)
+;;; c-ts-mode-tests.el ends here