Landscape analysis of fitness functions is an important topic. This paper makes an attempt to characterize the search problems associated with the fitness functions used in search-based testing, employing the following measures: diameter, autocorrelation and fitness distance correlation. In a previous work, a general form of objective functions for structural search-based software testing was tailored for state-based testing. A comparison is performed in this paper between the general fitness functions and some problem-specific fitness functions, taking into account their performance with different search methods.