patch 9.1.0765: No test for patches 6.2.418 and 7.3.489

Problem:  No test for patches 6.2.418 and 7.3.489
Solution: Add a test.  Fix some whitespace problems in test_mapping.vim.
          Document the behavior (zeertzjq).

closes: #15815

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index 93db940..7a00135 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -6581,8 +6581,8 @@
   call XbufferTests_range('l')
 endfunc
 
-" Test for displaying fname pass from setqflist when the name
-" are hard links to prevent seemly duplicate entries.
+" Test for displaying fname passed from setqflist() when the names include
+" hard links to prevent seemingly duplicate entries.
 func Xtest_hardlink_fname(cchar)
   call s:setup_commands(a:cchar)
   %bwipe