A method, apparatus and computer-implemented method, the method comprising: receiving a combinatorial testing model comprising an attribute collection, the attribute collection comprising a predetermined number of initial attributes, one or more possible values for each of the initial attributes, a coverage requirement, and an order coverage requirement for the initial attributes, the order coverage requirement related to predetermined relative order in which the attribute values are to be applied; and providing two or more tests in which each of the initial attributes is assigned a value from the possible values, wherein the tests satisfy the order coverage requirement for the at least two attributes.