Ensure that the file_directory_temp() function always returns a value.
function testFileDirectoryTemp() {
// Start with an empty variable to ensure we have a clean slate.
$config = config('system.file');
$config
->set('path.temporary', '')
->save();
$tmp_directory = file_directory_temp();
$this
->assertEqual(empty($tmp_directory), FALSE, 'file_directory_temp() returned a non-empty value.');
$this
->assertEqual($config
->get('path.temporary'), $tmp_directory);
}