The article discusses problems of model based test construction and ways of their solution using different kinds of models (operational, contract, axiomatic, and history-based specifications). The main idea is that the integration of model based techniques having different underlying formalisms can give valuable practical results in test construction. The idea is illustrated by successful applications of UniTesK test development technology based on the combination of contract specifications used to describe system behavior and operational models used for test sequence generation. UniTesK was designed in RedVerst [1] group of ISP RAS on the base of experience obtained in several industrial software testing projects.