1. A method executable on one or more processors for modeling a test space, the method comprising: defining a coverage model including: one or more variables, wherein respective values for the variables are assigned, and one or more definitions for value combinations for said variables with assigned values, wherein at least one of said value combinations is defined as optional, and zero or more other said value combinations are defined as forbidden or mandatory for purpose of generating test scenarios to test a system for which the coverage model is defined.