public function testNormalizeKeyDelimiters()
 {
     // Test data
     $header = 'Access_Control Allow-Origin';
     $canonicalized_key = HeaderDataCollection::normalizeKeyDelimiters($header);
     $this->assertNotSame($header, $canonicalized_key);
     $this->assertSame('Access-Control-Allow-Origin', $canonicalized_key);
 }