patch 8.2.2979: not all options code is covered by tests

Problem:    Not all options code is covered by tests.
Solution:   Add more tests for options. (Yegappan Lakshmanan, closes #8369)
diff --git a/src/testdir/test_mksession.vim b/src/testdir/test_mksession.vim
index 66e6e29..a0a2cb4 100644
--- a/src/testdir/test_mksession.vim
+++ b/src/testdir/test_mksession.vim
@@ -1019,6 +1019,19 @@
   endfor
 
   call s:ClearMappings()
+
+  " the 'pastetoggle', 'wildchar' and 'wildcharm' option values should be
+  " stored as key names in the vimrc file
+  set pastetoggle=<F5>
+  set wildchar=<F6>
+  set wildcharm=<F7>
+  call assert_fails('mkvimrc Xtestvimrc')
+  mkvimrc! Xtestvimrc
+  call assert_notequal(-1, index(readfile('Xtestvimrc'), 'set pastetoggle=<F5>'))
+  call assert_notequal(-1, index(readfile('Xtestvimrc'), 'set wildchar=<F6>'))
+  call assert_notequal(-1, index(readfile('Xtestvimrc'), 'set wildcharm=<F7>'))
+  set pastetoggle& wildchar& wildcharm&
+
   call delete('Xtestvimrc')
 endfunc