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_packadd.vim b/src/testdir/test_packadd.vim
index 6d0565b..fcb8b80 100644
--- a/src/testdir/test_packadd.vim
+++ b/src/testdir/test_packadd.vim
@@ -264,6 +264,8 @@
   call assert_match('look-here', tags1[0])
   let tags2 = readfile(docdir2 . '/tags') 
   call assert_match('look-away', tags2[0])
+
+  call assert_fails('helptags abcxyz', 'E150:')
 endfunc
 
 func Test_colorscheme()
@@ -355,3 +357,5 @@
   runtime! ALL extra/bar.vim
   call assert_equal('runstartopt', g:sequence)
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab