patch 8.2.0535: regexp patterns not fully tested

Problem:    Regexp patterns not fully tested.
Solution:   Add more regexp tests and others. (Yegappan Lakshmanan,
            closes #5901)
diff --git a/src/testdir/test_marks.vim b/src/testdir/test_marks.vim
index 15be080..fcae2ac 100644
--- a/src/testdir/test_marks.vim
+++ b/src/testdir/test_marks.vim
@@ -207,6 +207,9 @@
   call assert_fails('mark xx', 'E488:')
   call assert_fails('mark _', 'E191:')
   call assert_beeps('normal! m~')
+
+  call setpos("'k", [0, 100, 1, 0])
+  call assert_fails("normal 'k", 'E19:')
 endfunc
 
 " Test for :lockmarks when pasting content