1. A method for determining a series (S) of one or more code units within program code, comprising: first determining, by a processor, a plurality of series of code units, wherein for each series of code units, if any one of the code units of the series is executed, then each code unit of the series is executed; identifying, by the processor, at least one series (So) of the plurality of series of code units, wherein So includes an invocable program block, the invocable program block comprising a set of one or more invocable program elements, wherein the invocable program block has at least one statement that invokes at least one invocable program element, wherein the invocable program element includes one or more members of a group consisting of a function call, a method call, a program call, another invocable program element, and combinations thereof; second determining, by the processor, a grouping of one or more code units for each of the invocable program elements in the set, wherein the grouping includes at least some of the code units for at least one execution path from a starting code unit for the respective invocable program element to an ending code unit for the respective invocable program element; executing, by the processor, a relaxed priority estimation, wherein the relaxed priority estimation determines a priority value as a number of code lines that at least will be executed without determining which specific code line will be executed; based on the relaxed priority estimation, third determining, by the processor, a value for at least one of: the invocable program block and each of the invocation program blocks in the set; and determining, by the processor, the series S as one of the plurality of series, wherein S is related to the value.