patch 8.2.3744: E854 is not tested; some spelling suggestions are not tested

Problem:    E854 is not tested; some spelling suggestions are not tested.
Solution:   Add a couple of tests. (Dominique Pellé, closes #9279)
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 585b199..6fc4564 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -136,6 +136,12 @@
   set path&
 endfunc
 
+func Test_path_too_long()
+  exe 'set path=' .. repeat('x', 10000)
+  call assert_fails('find x', 'E854:')
+  set path&
+endfunc
+
 func Test_signcolumn()
   CheckFeature signs
   call assert_equal("auto", &signcolumn)