patch 8.2.0426: some errors were not tested for

Problem:    Some errors were not tested for.
Solution:   Add tests. (Dominique Pelle, closes #5824)
diff --git a/src/testdir/test_buffer.vim b/src/testdir/test_buffer.vim
index 3266adc..76fb04b 100644
--- a/src/testdir/test_buffer.vim
+++ b/src/testdir/test_buffer.vim
@@ -144,6 +144,7 @@
 func Test_bdelete_cmd()
   %bwipe!
   call assert_fails('bdelete 5', 'E516:')
+  call assert_fails('1,1bdelete 1 2', 'E488:')
 
   " Deleting a unlisted and unloaded buffer
   edit Xfile1