1. A system for facilitating programmable coverage domains, comprising: a domain definition input file; user-defined coverage domain data entered into said domain definition input file; a parser operable for translating said user-defined coverage domain data into machine-readable computer program code; an internal coverage domain comprising: a union of enabled coverage domains extracted from said user-defined coverage domain data; a session component comprising a session update count for each domain element; and a history component comprising a history update count for each domain element; and a testcase generator including an internal coverage feedback and measurement system, said testcase generator comprising: an instruction generator operable for generating instructions for use in a testcase; and an instruction simulator operable for simulating execution of said instructions; wherein said testcase generator accesses information in said internal coverage domain via said internal coverage feedback and measurement system, said internal coverage domain guiding testcase selections and updating said internal coverage domain according to results of testcase executions.