1. A method performed by a processor, comprising: obtaining user defined distribution traits characterizing a random sub-space of a space of assignments for a set of generative variables; applying the user defined distribution traits on the space of assignments for a set of generative variables to generate the random sub-space of the space of assignments for a set of generative variables; and testing a device under test using the generated random sub-space of the space of assignments for a set of generative variables.