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diff --git a/test/lisp/jit-lock-tests.el b/test/lisp/jit-lock-tests.el
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+++ b/test/lisp/jit-lock-tests.el
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+;;; jit-lock-tests.el --- tests for jit-lock
+
+;; Copyright (C) 2016 Free Software Foundation, Inc.
+
+;; Author: Dmitry Gutov <dgutov@yandex.ru>
+
+;; 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 <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;; Code:
+
+(require 'jit-lock)
+(require 'ert-x)
+
+(defun jit-lock-tests--setup-buffer ()
+  (setq font-lock-defaults '(nil t))
+  (let (noninteractive)
+    (font-lock-mode)))
+
+(ert-deftest jit-lock-fontify-now-fontifies-a-new-buffer ()
+  (ert-with-test-buffer (:name "xxx")
+    (jit-lock-tests--setup-buffer)
+    (insert "xyz")
+    (jit-lock-fontify-now (point-min) (point-max))
+    (should-not (text-property-not-all (point-min) (point-max) 'fontified t))))
+
+(ert-deftest jit-lock-fontify-now-mends-the-gaps ()
+  (ert-with-test-buffer (:name "xxx")
+    (jit-lock-tests--setup-buffer)
+    (insert "aaabbbcccddd")
+    (with-silent-modifications
+      (put-text-property 1 4 'fontified t)
+      (put-text-property 7 10 'fontified t))
+    (jit-lock-fontify-now (point-min) (point-max))
+    (should-not (text-property-not-all (point-min) (point-max) 'fontified t))))
+
+(ert-deftest jit-lock-fontify-now-does-not-refontify-unnecessarily ()
+  (ert-with-test-buffer (:name "xxx")
+    (setq font-lock-defaults
+          (list '(((lambda () (error "Don't call me")))) t))
+    (let (noninteractive)
+      (font-lock-mode))
+    (insert "aaa")
+    (with-silent-modifications
+      (put-text-property (point-min) (point-max) 'fontified t))
+    (jit-lock-fontify-now (point-min) (point-max))))