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