function testCanMergeUniquely()
{
$this->assertSame(['a', 'b'], elgg_extract_class(['class' => 'b'], 'a'));
$this->assertSame(['a', 'b'], elgg_extract_class(['class' => ['a', 'b']], 'a'));
$this->assertSame(['a', 'b', 'c', 'd'], elgg_extract_class(['class' => ['c', 'd']], ['a', 'b']));
}