patch 8.2.0174: various commands not completely tested

Problem:    Various commands not completely tested.
Solution:   Add more test cases. (Yegappan Lakshmanan, closes #5551)
diff --git a/src/testdir/test_fnameescape.vim b/src/testdir/test_fnameescape.vim
index b0fdb3a..cdb96ba 100644
--- a/src/testdir/test_fnameescape.vim
+++ b/src/testdir/test_fnameescape.vim
@@ -18,4 +18,10 @@
   endtry
   call assert_true(status, "ExclamationMark")
   call delete(fname)
+
+  call assert_equal('\-', fnameescape('-'))
+  call assert_equal('\+', fnameescape('+'))
+  call assert_equal('\>', fnameescape('>'))
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab