use Foo::Test::LogMessages;
my $log = Foo::Test::LogMessages->new;

sub TEST_WHICH_HAS_LOG_OUTPUT
{
  # do something
  $log->capture_log_only_for_this_scope;
  is($log->message, qw/some message/, '... and we should have an error');
}

sub TEST_WHICH_DOES_NOT_HAVE_LOG_OUTPUT
{
  # do something
}