diff --git a/src/testdir/test_ruby.vim b/src/testdir/test_ruby.vim
index cc5f419..d4ff8e0 100644
--- a/src/testdir/test_ruby.vim
+++ b/src/testdir/test_ruby.vim
@@ -446,7 +446,10 @@
   ruby << trim eof
     Vim.command('let s ..= "E"')
   eof
-  call assert_equal('ABCDE', s)
+ruby << trimm
+Vim.command('let s ..= "F"')
+trimm
+  call assert_equal('ABCDEF', s)
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab