# Systematic Literature Review on Test Case Selection and Prioritization: A Tertiary Study
## 4 Results and Analysis
### RQ2. To Study the Characteristics of Secondary Studies  
_RQ 2.1: Which research approaches have been used by various secondary studies?_  
Reviewing primary texts can be accomplished via various techniques. The most commonly used methods are SLR, systematic mappings, and non-systematic surveys/reviews. The difference in performing SLR and mappings is discussed in Section 1. These are systematic approaches with available guidelines to be followed for searching and selecting the studies for review. Due to the systematic approach, these techniques take a large amount of time and effort to complete the review process. Many reviews may not claim to include all the studies in the relevant field or to provide conclusions after analysis. Such texts are  
Figure 4: Publication type. Figure 3: Number of surveys in TCS&P published per year. very helpful in providing insights into various aspects and the collection of primary texts available in the reviewed area. Moreover, they consume comparatively less time and effort. Many researchers have adopted this approach for performing literature reviews, surveying particular aspects, and analyzing and depicting trends. All of these texts were classified to the survey/review category. Figure 5 provides the classification of the reviewed 22 studies into three types: eight SLRs, three mappings, and one paper claiming to be comprise both an SLR and a mapping. Ten studies were surveys/reviews but not SLRs or mapping studies. Figure 6 depicts publishing trends for these three types of surveys in TCS&P. Publishing trends for mappings are marked as 0 or 1 in a year. There was an apparent increase in the number of SLRs and reviews/surveys in TCS&P after 2015. The growing interest of the research community in the field of TCS&P can be inferred from these publication trends. \begin{table}
\begin{tabular}{l c} \hline \hline
**Name of the Journal** & **NS** \\ \hline Information \& Software Technology & 3 \\ Informatica & 2 \\ International Journal of Software Engineering and Knowledge Engineering & 2 \\ IEEE Access & 2 \\ Software Testing, Verification, and Reliability & 1 \\ Software Quality Journal & 1 \\ Frontiers of Computer Science & 1 \\ ACM Computing Surveys & 1 \\ Journal of King Saud University & 1 \\ International Journal of Engineering \& Technology & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Journals in which secondary studies were TCS&P published. Figure 5: Classification of selected 22 secondary studies. **RQ 2.2:**_What are the focus and the range of years covered in the secondary studies?_  
Figure 7 uses the radar plot to represent the same years covered by the studies. It shows the beginning and the ending year of respective searches conducted in the studies (identified as S1 to S22). It was found that all surveys or review papers (fitting our inclusion criteria) were published after 2010. Hence the outer circle, which represents the end year of the search, encompasses a decade (2010-2020). One of the studies (S22) was undertaken after another existing study; hence the search years ranged only from 2017 to 2019. Surveys performed over comparable year ranges must include almost the same texts. Similarly, future researchers can explore the primary studies lying outside the outer plot presented in Figure 7.  
The 22 studies either focused on TCS, TCP, or a combination of both. Figure 8 shows how the majority of the secondary texts (82%) focused on TCP, whereas only 32% focused on TCS. Figure 6: Types of surveys published by year. Figure 7: Years covered in the 22 secondary studies for the survey. Research in the area of TCP began in 1997 [3], whereas that of TCS began in 1988 [62]. The surveys conducted after these studies used information gathered in these papers, so they needed to cover a reduced number of years. As is evident from Figure 7, most of the surveys were been conducted over the last two decades (2000-2020).