patch 8.0.0912: cannot run a job in a hidden terminal

Problem:    Cannot run a job in a hidden terminal.
Solution:   Add option "hidden" and ++hidden.
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index 9012bec..97c13ef 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -337,7 +337,6 @@
   endif
 
   exe 'terminal ++close ' . cmd
-  let buf = bufnr('')
   call assert_equal(2, winnr('$'))
   wincmd p
   call WaitFor("winnr('$') == 1", waittime)
@@ -345,24 +344,32 @@
 
   call term_start(cmd, {'term_finish': 'close'})
   call assert_equal(2, winnr('$'))
-  let buf = bufnr('')
   wincmd p
   call WaitFor("winnr('$') == 1", waittime)
   call assert_equal(1, winnr('$'))
 
   exe 'terminal ++open ' . cmd
-  let buf = bufnr('')
   close
   call WaitFor("winnr('$') == 2", waittime)
   call assert_equal(2, winnr('$'))
   bwipe
 
   call term_start(cmd, {'term_finish': 'open'})
-  let buf = bufnr('')
   close
   call WaitFor("winnr('$') == 2", waittime)
   call assert_equal(2, winnr('$'))
+  bwipe
 
+  exe 'terminal ++hidden ++open ' . cmd
+  call assert_equal(1, winnr('$'))
+  call WaitFor("winnr('$') == 2", waittime)
+  call assert_equal(2, winnr('$'))
+  bwipe
+
+  call term_start(cmd, {'term_finish': 'open', 'hidden': 1})
+  call assert_equal(1, winnr('$'))
+  call WaitFor("winnr('$') == 2", waittime)
+  call assert_equal(2, winnr('$'))
   bwipe
 endfunc