The practice exam for HDP Certified Developer is found here: http://hortonworks.com/training/class/hdp-certified-developer-hdpcd-exam/
On the right-hand column of that page, click on the PDF file named “HDPCD-PracticeExamGuide”: http://hortonworks.com/wp-content/uploads/2015/02/HDPCD-PracticeExamGuide1.pdf