patch 8.2.1022: various parts of code not covered by tests

Problem:    Various parts of code not covered by tests.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #6300)
diff --git a/src/testdir/test_selectmode.vim b/src/testdir/test_selectmode.vim
index 92951ef..3adb843 100644
--- a/src/testdir/test_selectmode.vim
+++ b/src/testdir/test_selectmode.vim
@@ -38,6 +38,9 @@
   set selectmode=cmd
   call feedkeys('gvabc', 'xt')
   call assert_equal('abctdef', getline(1))
+  " arrow keys without shift should not start selection
+  call feedkeys("A\<Home>\<Right>\<Left>ro", 'xt')
+  call assert_equal('roabctdef', getline(1))
   set selectmode= keymodel=
   bw!
 endfunc