patch 8.1.1336: some eval functionality is not covered by tests

Problem:    Some eval functionality is not covered by tests.
Solution:   Add a few more test cases. (Masato Nishihata, closes #4374)
diff --git a/src/testdir/test_delete.vim b/src/testdir/test_delete.vim
index 4686a0d..b3e153e 100644
--- a/src/testdir/test_delete.vim
+++ b/src/testdir/test_delete.vim
@@ -105,3 +105,8 @@
   bwipe Xdir3/subdir/Xfile
   bwipe Xdir4/Xfile
 endfunc
+
+func Test_delete_errors()
+  call assert_fails('call delete('''')', 'E474:')
+  call assert_fails('call delete(''foo'', 0)', 'E15:')
+endfunc