1. A method for determining a series (S) of one or more code units within software code to execute, comprising: a processor obtaining a representation of a graph, wherein the graph corresponds to a flow graph for the software code, and each node of the graph corresponds to a series of code units of the software code, wherein if any one of the code units of the series is executed, then each code unit of the series is executed; the processor determining one or more acyclic executable paths through the graph from a predetermined starting node of the graph to a predetermined ending node of the graph, wherein the acyclic executable path includes two or more nodes; the processor determining, for each of the nodes of the graph, a corresponding weight, wherein the weight of the node is indicative of at least a minimum number of code units executed when executing code units identified by the node; the processor determining, for each of the acyclic executable paths, a corresponding path weight, wherein for each executable path (P) having a path weight (Wte), the path weight Wte is related to a combination of the weights of the nodes of the executable path P; the processor determining, for each node (N) of the graph, a corresponding priority using the path weight for each of the executable paths containing N; and the processor determining the series S of code units from the corresponding priorities of the nodes.