1. A computer-implemented method comprising: obtaining, by a computer, a combinatorial model for functional coverage analysis of a system under test, the combinatorial model defining a legal test space that is an aggregation of coverage tasks that can be tested, the combinatorial model comprising a set of attributes, a respective domain for each attribute defining possible values for the attribute, and a set of restrictions, wherein the restrictions define a combination of values of the attributes that are illegal and are excluded from the legal test space; obtaining, by the computer, a partially illegal combination defining value assignments to a portion of the attributes; automatically identifying, by the computer, an extension of the partially illegal combination and a modification that will render the extension legal, wherein the extension is excluded from the legal test space, wherein the modification changes a portion of the value assignments defined by the partially illegal combination, wherein the automatically identifying comprises utilizing a Binary Decision Diagram (BDD), and wherein the utilizing of the BDD comprises: encoding a first BDD representing all extensions of the partially illegal combination that are excluded from the legal test space; existing out from the first BDD all BDD variables that correspond to the portion of the attributes to which the partially illegal combination assigns values to compute a second BDD; and conjuncting the second BDD with the legal test space to compute a third BDD; and outputting, by the computer, an indication of the extension and the modification.
1. A computer-implemented method comprising: obtaining, by a computer, a combinatorial model for functional coverage analysis of a system under test, the combinatorial model defining a legal test space that is an aggregation of coverage tasks that can be tested, the combinatorial model comprising a set of attributes, a respective domain for each attribute defining possible values for the attribute, and a set of restrictions, wherein the restrictions define a combination of values of the attributes that are illegal and are excluded from the legal test space; obtaining, by the computer, a partially illegal combination defining value assignments to a portion of the attributes; automatically identifying, by the computer, an extension of the partially illegal combination and a modification that will render the extension legal, wherein the extension is excluded from the legal test space, wherein the modification changes a portion of the value assignments defined by the partially illegal combination, wherein the automatically identifying comprises utilizing a Binary Decision Diagram (BDD), and wherein the utilizing of the BDD comprises: encoding a first BDD representing all extensions of the partially illegal combination that are excluded from the legal test space; existing out from the first BDD all BDD variables that correspond to the portion of the attributes to which the partially illegal combination assigns values to compute a second BDD; and conjuncting the second BDD with the legal test space to compute a third BDD; and outputting, by the computer, an indication of the extension and the modification. 2. The computer-implemented method of claim 1 , wherein said utilizing the BDD further comprises: selecting one combination defined by the third BDD, and wherein the one combination that is selected corresponds to the extension.