Context: Any newcomer or industrial practitioner is likely to experience difficulties in digesting large volumes of knowledge in software testing. In an ideal world, all knowledge used in industry, education and research should be based on high-quality evidence. Since no decision should be made based on a single study, secondary studies become essential in presenting the evidence. According to our search, over 101 secondary studies have been published in the area of software testing since 1994. With this high number of secondary studies, it is important to conduct a review in this area to provide an overview of the research landscape in this area.