The article presents an authorial method of synthesizing vehicle-driving tests for determining, by rig testing, performance characteristics of internal combustion (IC) engines in dynamic states representative for the conditions of real engine operation. The method of synthesizing such tests is based on the criteria of similarity between characteristics of the physical quantities that describe the state of engine operation. The similarity criteria apply to the tasks performed by the engine and defined as the consecutive engine operation conditions and the corresponding engine operation states, each representing an elementary action performed by the engine operator by means of the engine. An example synthesis of a test has been presented for the engine speed in the IC engine operation conditions corresponding to the FTP-75 test cycle. The tests built in accordance with the method presented show good repeatability for the empirical data corresponding to various engine speed realizations in the vehicle-driving test.