Add simple tests for the `fill-polish-nobreak-p' function

* test/lisp/textmodes/fill-tests.el:
(fill-test-no-fill-polish-nobreak-p): New test

test/lisp/textmodes/fill-tests.el

@@ -0,0 +1,50 @@
+;;; fill-test.el --- ERT tests for fill.el -*- lexical-binding: t -*-
+
+;; Copyright (C) 2017 Free Software Foundation, Inc.
+
+;; Author:     Marcin Borkowski <mbork@mbork.pl>
+;; Keywords:   text, wp
+
+;; 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/>.
+
+;;; Commentary:
+
+;; This package defines tests for the filling feature, specifically
+;; the `fill-polish-nobreak-p' function.
+
+;;; Code:
+
+(require 'ert)
+
+(ert-deftest fill-test-no-fill-polish-nobreak-p nil
+  "Tests of the `fill-polish-nobreak-p' function."
+  (with-temp-buffer
+    (insert "Abc d efg (h ijk).")
+    (setq fill-column 8)
+    (setq-local fill-nobreak-predicate '())
+    (fill-paragraph)
+    (should (string= (buffer-string) "Abc d\nefg (h\nijk).")))
+  (with-temp-buffer
+    (insert "Abc d efg (h ijk).")
+    (setq fill-column 8)
+    (setq-local fill-nobreak-predicate '(fill-polish-nobreak-p))
+    (fill-paragraph)
+    (should (string= (buffer-string) "Abc\nd efg\n(h ijk)."))))
+
+
+(provide 'fill-tests)
+
+;;; fill-tests.el ends here