/**
*
*/
public function testMergerKeysNormalization()
{
$collection = new Collection(['X' => 'a', 'y' => 'b', 'Z' => 'C']);
$collection->addKeyNormalizer(function (&$key) {
$key = strtoupper($key);
});
$merger = $this->getMockBuilder(ValueMerger::class)->disableOriginalConstructor()->getMock();
$collection->addMerger('lowercase', $merger);
$this->assertArrayHasKey('LOWERCASE', $collection->getMergers());
}