reflection.php

<?php

// ...

public function testProtected()
{
	$dateFormatter = new DateFormatter;

	$class = new \ReflectionClass('DateFormatter');

    	// Find the protected/private method and make it public
	$getSentence = $class->getMethod('getSentence');
	$getSentence->setAccessible(true);

    	// Trigger the method, and pass in any applicable args
	$sentence = $getSentence->invokeArgs($dateFormatter, [1, 'month']);
    
	// Do your test as usual
	$this->assertEquals('1 month from now.', $sentence);
}