patch 8.2.0203: :helptags and some other functionality not tested

Problem:    :helptags and some other functionality not tested.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5567)
diff --git a/src/testdir/test_filechanged.vim b/src/testdir/test_filechanged.vim
index bfcdb76..6d17d95 100644
--- a/src/testdir/test_filechanged.vim
+++ b/src/testdir/test_filechanged.vim
@@ -138,7 +138,7 @@
   sleep 2
   silent !touch Xchanged_d
   let v:warningmsg = ''
-  checktime
+  checktime Xchanged_d
   call assert_equal('', v:warningmsg)
   call assert_equal(1, line('$'))
   call assert_equal('new line', getline(1))