1. A method executable on one or more processors for modeling a test space, the method comprising: defining a Cartesian-product model, wherein the Cartesian-product model includes one or more variables, wherein respective values for the variables are assigned to define a test space for a system under test, and restrictions based on which valid variable value combinations are determined for the purpose of testing the Cartesian-product model; identifying a first value for a first variable of the one or more variables in coverage requirements of the Cartesian-product model; identifying a second value for the first variable of the one or more variables in coverage requirements of the Cartesian-product model; determining that the identified first value for the first variable and the identified second value for the first variable are equivalent for the purpose of testing the Cartesian-product model, wherein the first value for the first variable is determined to be equivalent to the second value for the first variable if assigning of either the first value for the first variable or the second value for the first variable to the first variable in the Cartesian-product model results in no change in validity or invalidity status of variable value combinations in the Cartesian-product model; and merging the first value for the first variable and the second value for the first variable to create a third value for the first variable, wherein the Cartesian-product model utilizes the third value for the first variable for coverage requirements in exchange for both the first value for the first variable and the second value for the first variable.