patch 8.2.1183: assert_fails() checks the last error message
Problem: assert_fails() checks the last error message.
Solution: Check the first error, it is more relevant. Fix all the tests
that rely on the old behavior.
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index c7229fc..381a2c1 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -367,7 +367,7 @@
setlocal completefunc=DummyCompleteTwo
call setline(1, 'two')
/^two
- call assert_fails('call feedkeys("A\<C-X>\<C-U>\<C-N>\<Esc>", "x")', 'E764:')
+ call assert_fails('call feedkeys("A\<C-X>\<C-U>\<C-N>\<Esc>", "x")', 'E839:')
call assert_notequal(winid, win_getid())
q!
call assert_equal(winid, win_getid())