A Comprehensive Bibliometric Assessment on Software Testing (2016–2021)

: The research study provides a comprehensive bibliometric assessment in the ﬁeld of Software Testing (ST). The dynamic evolution in the ﬁeld of ST is evident from the publication rate over the last six years. The research study is carried out to provide insight into the ﬁeld of ST from various research bibliometric aspects. Our methodological approach includes dividing the six-year time frame into the set of two symmetric but different periods (2016–2018) and (2019–2021) comprising a total of 75,098 records. VOSViewer is used to perform analysis with respect to collaboration network of countries and co-word assessment. Bibliometrix (Studio R) analysis tool is used to evaluate research themes/topics. The year 2019 leads the publication rate whereas a decrement in publication frequency is observed for the years 2020 and 2021. Our research study shows the inﬂuence of ST in other research domains as depicted in different research areas. Especially the impact of ST in the Electrical and Electronics Domain is quite notable. Most of the research publications are from the USA and China as they are among the most resourceful countries. On the whole, the majority of the publications are from Asian countries. Collaboration networks amongst countries demonstrate the fact that the higher the collaboration network, the greater would be the research output. Co-word analysis presents the relatedness of documents based on the keywords. The topic dendrogram is generated based on the identiﬁed research themes. Although English is the leading language, prominent studies are present in other languages also. This research study provides a comprehensive analysis based on 12 informative research questions


Introduction
It has been more than 45 years since the foundation of software engineering (SE) [1]. In 1968, at the NATO Software Engineering Conference the phrase "software engineering" was used for the first time [1,2]. SE refers to the concepts, techniques, and methods or approaches used in the development of software in computer systems [3,4]. The development and implementation of large and sophisticated systems, technical advancements, and the development of sub-areas highlight the significance of the SE field. SE consists of methodologies, processes, and the use of appropriate methods to produce high-quality computer software in the required time frame [5]. SE is defined as a set of procedures (processes) for managing and developing software-intensive systems, either individually or collectively (as a team) [6]. Software engineering as a research approach is distinct from the techniques, methods, and approaches employed in software development [7].
One of the important areas of SE is Software Testing (ST). The set of process activities is specially designed to ensure validity and verifies the software that is being developed so that the software is designed in such a way that it matches the business and technical requirements [8]. In other words, ST regulates the unintended behaviors of the software systems. ST plays a fundamental role in the development life cycle of software [9]. Improper testing can lead to major risks and unexpected outcomes [9]. Because ST is a single strategy to ensure software quality, it consumes most development resources. However, ST is a costly and time-consuming process. As a result, testing should start as soon as possible in the development phase to avoid financial and time constraints. Even so, testing should be carried out at each stage of the software development life cycle [10].
ST is widely classified as functional and non-functional testing [11]. The two types of testing approaches that are widely deployed in the testing world are black-box testing and white-box testing. Both can be found in a variety of software testing procedures. The input and output are the only considerations in black-box testing, which ignores the block's internal design and functionality. The black-box approach focuses on analyzing the software's performance in response to a specific input. The white-box approach, on the other hand, focuses on the block's internal development and performance. It is the goal of the white-box technique to trace and discover all of the paths taken by a given input as it makes its way through the software [12]. Grey-box testing has been explored as a third testing approach in recent years. It is characterized as software testing combined with some understanding of the internal logic and underlying code. It employs internal data structures and algorithms to generate test cases to a greater extent than black-box testing, but not nearly as much as white-box testing [13]. The most common type of ST strategy is Integration testing. This approach is considered when more than one component is integrated into a more prominent model. This is carried out if the quality attribute cannot be accurately assessed from its parts; this testing is frequently performed in the interfaces between the components and the structure produced [13]. Another common type of testing is System Testing, which incorporates analysis based on the whole system's quality testing. System testing is often functional and requires the specifications of the system [13]. Acceptance testing is carried out when the entire system is turned over to customers or users from the development side. Acceptance testing aims to ensure that the system is operational rather than to identify problems [8]. Unit testing evaluates the foundational unit of software application. It is only one of the testing steps that contribute to the aim of analyzing a system. It is frequently referred to as a white-box test class [13]. Test cases are used to carry out different types of tests [12].
The influence of ST is not only limited to the SE field, but has a vast impact on other areas as well. ST plays a vital role in web and application testing [12], testing of various embedded devices with respect to nuclear power applications [14], applications that are cloud-based [15], and testing of various aspects of smart contracts in blockchain [16], testing IoT applications [17].
ST plays an important role in the development and architectural aspects of software. In both centralized and distributed contexts, the 1 + 5 model has known to be a great framework for the design of enterprise service bus (ESB) as well as the distributed blockchain solutions [18]. This study [18] focuses on the integration aspect to propose an architectural approach for designing solutions that ensures that all parties involved in the communication are aligned. Various ST techniques are involved in Continuous Software Engineering (CSE) which is a new field of study and practice. CSE refers to the rapid development, deployment, and feedback from applications and customers. There are three steps of CSE: business strategy & planning, development, and operations [19]. Continuous Integration, Continuous Delivery, and Continuous Deployment are different aspects of the development phase with respect to CSE. Testing techniques are involved in various applications which require continuous delivery specifically for those applications that are blockchain-based [20]. In the scope of Continuous Delivery and Deployment, live testing is performed to test modifications or new features in the production system. Canary releases, dark launches, A/B tests, and gradual rollouts are all examples of this. Several of these live testing techniques are frequently coupled with each other [21]. The involvement of customers in the testing phase of Continuous Deployment is proposed in the study [19]. For Continuous Integration, the study [19] proposes multiple aspects of ST such as development based on test-driven approaches, planning of multiple tests, testing approaches based on cross-team activity, while decoupling of unit tests from acceptance tests as well as from the functional tests should be practiced. The main purpose of these ST techniques is to ensure the development of software that is thoroughly tested to guarantee that it meets the software requirements and is correctly developed.
The approach of showing and comparing numerous quantifiable facts required for studying evaluation is known as bibliometric assessment [22,23]. Scholars, researchers, and students can benefit from bibliometric analysis by using it to make better decisions in their respective fields based on various characteristics and by using it to spur additional research in areas where it is needed.
In addition to the powerful tools, the introduction of scientific databases such as Web of Science has allowed the acquisition of massive data to undertake a thorough bibliometric study. VOSViewer and Bibliometrix(R studio) are the two most commonly used platforms that allow to execute quantitative analysis and create a map of all scientific knowledge Section 1 of our research study deals with the introduction, whereas Section 2 presents related work. The methodology is discussed in Section 3. Research findings and discussion constitute Section 4. Section 5 briefly states the future work and limitations of our study, whereas the conclusion is presented in Section 6. Finally, references are presented in the last section.

Related Work
The eminent research studies in the field of SE are summarized on the basis of parameters analyzed, time frames, and data sources as depicted in Table 1. To the best of our knowledge, the Software Testing field lacks such a comprehensive bibliometric assessment. Hence, all the related work presented in Table 1 belongs to the Software Engineering field. The details to be placed in Table 1 are carefully designed to provide a concise and easily understandable picture of the work presented in the included research studies. Our prominent contributions are listed in Table 2.  Research contribution based on the continent: Map-based representation depicting continent-wise research contribution in terms of publications is another aspect of our research study. Analysis based on co-word: Analysis on the basis of co-words that appear in different articles is presented in the study. The keywords play an important role in providing the basis for the evaluation of research topics/themes.

Representation of diversity in terms of publication medium:
We also present the top 20 languages used as the medium for publications in the field. This further affirms the fact that, although English is by far the most commonly used language for writing articles, other languages also contribute. This encourages non-English writers to make effective and valuable research contributions by writing in their language of fluency. Cross-disciplinary research areas: Our work includes findings based on cross-disciplinary research areas. Hence, this affirms the fact that the impact of ST goes beyond Computer Science and Software Engineering.

Methodology
This section presents a complete methodological process followed in our research work.

Creation of Two Distinguished Datasets for Two Different Time Spans
In order to conduct the bibliometric assessment, Web of Science (WoS) is used to acquire our required dataset for the years 2016-2021. The dataset is acquired from the WoS Core Collection. The ISI WoS is one of the most commonly used electronic databases provided by Thomson Scientific's Institute for Scientific Information [33] to perform bibliometric assessment which is also evident from Table 1. The initial dataset comprised 210,640 records for the query (Software AND Testing). However, refinement on the basis of topic is performed by selecting the topic while giving "Software AND Testing" as input in the query field. This is to ensure that all the articles included in the dataset are relevant to the topic of ST. Further refinement of datasets is carried out on the basis of inclusion/exclusion criteria as presented in Table 3. A complete methodological process is shown in Figure 1 for the formation of two distinguished data sets having 35,161 records for the years 2016-2018 and 39,937 records for the time frame 2019-2021.

Research Questions for the Analysis of Datasets
After extracting the dataset, this dataset is analyzed in accordance with the research questions. The connection between our research questions is our underlying research objective to find insights into the field of Software Testing with respect to various diverse aspects of bibliometric evaluation. We perform the analysis so as to determine and analyze the findings of the research questions such as the type of research documents, the yearwise rate of publications, the languages used as a medium to publish research studies, top 20 countries, and top 20 organizations based on these research studies, research areas, research themes, topic dendrogram used in conjunction with ST, the relatedness of documents in terms of co-word, and the impact of collaboration amongst countries in terms of the frequency of publications. Table 4 represents the analysis criteria for the two phases 2016-2018 and 2019-2021 in terms of formulated research questions. We have used builtin tools of the ISI Web of Science (WoS) database to evaluate Q1, Q3-Q9. VOSviewer is used as a visualization tool to map the findings related to Q10 and Q11. VOSviewer is a program that enables users to create maps based on network data and then visualize and explore them. VOSviewer is primarily meant for facilitating bibliometric assessment [34]. Bibliometrix is an app based on R which is used for the analysis of multiple aspects of bibliometrics. In our research work, we use this tool to perform various evaluations related to Q12 and Q2.

Insights
Research Questions

Research Questions for the Analysis of Datasets
After extracting the dataset, this dataset is analyzed in accordance with the research questions. The connection between our research questions is our underlying research objective to find insights into the field of Software Testing with respect to various diverse aspects of bibliometric evaluation. We perform the analysis so as to determine and analyze the findings of the research questions such as the type of research documents, the year-wise rate of publications, the languages used as a medium to publish research studies, top 20 countries, and top 20 organizations based on these research studies, research areas, research themes, topic dendrogram used in conjunction with ST, the relatedness of documents in terms of co-word, and the impact of collaboration amongst countries in terms of the frequency of publications. Table 4 represents the analysis criteria for the two phases 2016-2018 and 2019-2021 in terms of formulated research questions. We have used built-in tools of the ISI Web of Science (WoS) database to evaluate Q1, Q3-Q9. VOSviewer is used as a visualization tool to map the findings related to Q10 and Q11. VOSviewer is a program that enables users to create maps based on network data and then visualize and explore them. VOSviewer is primarily meant for facilitating bibliometric assessment [34]. Bibliometrix is an app based on R which is used for the analysis of multiple aspects of bibliometrics. In our research work, we use this tool to perform various evaluations related to Q12 and Q2.

Research Findings
This section deals with the research findings and a comprehensive discussion regarding the results of the research questions.

Research Findings
This section deals with the research findings and a comprehensive discussion reg ing the results of the research questions.    Figure 3 consists of more than 20 entries because multiple publication venues have the same number of publications, so they occupy the same position in the top 20. The darker the blue color is (in both the figures: Figures 3 and 4), the greater the number of publications these sources (publication venues) have.

Top 20 Publication Venues
The top 20 publication venues (sources of publications) for the two different time frames are shown in Figures 3 and 4. Figure 3 represents the top 20 publication venues for the time frame 2016-2018. During this time frame (2016-2018), the data set comprises a total of 12,090 publication venues whereas the total number of publication venues for 2019-2021 added up to 10,558. Figure 3 consists of more than 20 entries because multiple publication venues have the same number of publications, so they occupy the same position in the top 20. The darker the blue color is (in both the figures: Figures 3 and 4), the greater the number of publications these sources (publication venues) have.
These publication venues further affirm the fact that the impact of Software Testing is not only limited to the computing and software fields but expands across multi-disciplinary areas as evident from Figures 3 and 4.    Figure 5 represents the types of documents that belong to the two distinguished datasets. It is to be noted that a single research study tends to be a part of more than one type of document. To elaborate on this, a research study can be classified as an article as well as the proceeding's papers. Articles comprise a major portion of these publications.  These publication venues further affirm the fact that the impact of Software Testing is not only limited to the computing and software fields but expands across multi-disciplinary areas as evident from Figures 3 and 4. Figure 5 represents the types of documents that belong to the two distinguished datasets. It is to be noted that a single research study tends to be a part of more than one Electronics 2022, 11,1984 8 of 26 type of document. To elaborate on this, a research study can be classified as an article as well as the proceeding's papers. Articles comprise a major portion of these publications.  Figure 5 represents the types of documents that belong to the two distinguished da tasets. It is to be noted that a single research study tends to be a part of more than one typ of document. To elaborate on this, a research study can be classified as an article as we as the proceeding's papers. Articles comprise a major portion of these publications.    The influence of Software Testing across multiple disciplines is evident by the various distinct WoS categories such as Telecommunications, Mechanical Engineering, Multidisciplinary Engineering, Multidisciplinary Materials Science, Energy Fuels, Automation Control Systems, Civil Engineering, Multidisciplinary Sciences, General Internal Medicine, Applied Physics, Educational Research, Instrumentation, Environmental Sciences, Dentistry and Oral Surgery Medicine, and Radiology Nuclear Medical Imaging. The software developed in these fields requires Software Testing to provide validation and verification in accordance with the requirements of the software.

Top 20 Research Areas in Accordance with the Record Count of Publications
Research areas are article-based. The Research Area depicts the research areas present within a particular document. As a result, one can recognize, retrieve and evaluate documents from multiple databases that belong to the same subject. Tables 7 and 8  This feature represents that the application of ST is not only limited to Computer Science or Engineering fields, but ST plays an important role in the validation and verification of various other fields such as Medical, Education, Physics, Optics, Mathematics, Business Economics, Biochemistry Molecular Biology, Radiology Nuclear Medicine Medical Imaging, Chemistry, Environmental Sciences, Energy Fuels, Pharmacology, Automation Control Systems, and Construction Technology. Thus, the importance and impact of ST encompass multiple disciplinary areas which represent that the techniques, processes, methods, and approaches of ST are applicable in designing the application software related to other fields to confirm that the developed application is in accordance with the technical and customer requirements.   Tables 9 and 10. This assessment criterion helps scholars to identify the most contributing institutions/organizations in terms of research count in the field of ST for a period of the last six years. Throughout both the time frames, we analyzed that most publications were contributed by scholars having an affiliation with the Islamic Azad University, Iran. However, the USA leads in the number of institutions/organizations present in the top 20, followed by Iran, China, France, and India. The number of institutions/organizations in Tables 9 and 10 belonging to a specific country is shown in Figures 6 and 7 below. Throughout both the time frames, we analyzed that most publication uted by scholars having an affiliation with the Islamic Azad University, I the USA leads in the number of institutions/organizations present in the to by Iran, China, France, and India. The number of institutions/organizatio and 10 belonging to a specific country is shown in Figures 6 and 7 below.    (Tables 11 and 12) are a key factor in representing the most actively participating countries in the research area of ST over the last six years with respect to the number of publications. It is to be noted that in the case of multi-authored documents, contributions of all countries based upon authors' affiliations are considered. The results of Tables 11 and 12 state that the USA and China show more significant contributions than the rest of the countries as they are more developed and financially more strong countries. However, the results suggest that more Asian countries are partici-

Continent-Wise Research Contribution
The continent-wise research contribution as per the record count of published studies is shown in Figures 8 and 9 for the years 2016-2018 and 2019-2021. It is to be noted that in the case of multi-authored documents, contributions of all countries based upon authors' affiliations are considered.  It is evident from the figures (Figures 8 and 9) that for the time frame (2016-2018), Europe was leading as the continent which makes the most research contributions with respect to the number of publications. During this time frame, Asia was the second most contributing continent as far as the research aspect is concerned in the field of ST relative to the number of publications. However, for the time duration (2019-2021), Asia contributed the most in terms of research publications in the field of ST, with Europe contributing to research publications in the second place in ST. The rise in the number of published articles from Africa and Australia is also evident. The publication contribution of Asian countries has a significant rise from approx. 34% to approx. 38% of the total published scholarly studies.   It is evident from the figures (Figures 8 and 9) that for the time frame (2016-2018), Europe was leading as the continent which makes the most research contributions with respect to the number of publications. During this time frame, Asia was the second most contributing continent as far as the research aspect is concerned in the field of ST relative to the number of publications. However, for the time duration (2019-2021), Asia contributed the most in terms of research publications in the field of ST, with Europe contributing to research publications in the second place in ST. The rise in the number of published articles from Africa and Australia is also evident. The publication contribution of Asian countries has a significant rise from approx. 34% to approx. 38% of the total published scholarly studies. It is evident from the figures (Figures 8 and 9) that for the time frame  English is found to take about 99 percent of the complete pool of the value work included in our research study. The conclusions that are drawn from the table show us that the contributions of the researchers in different languages are significant. The articles published in languages other than English facilitate the researchers in disseminating the knowledge to non-English speakers. Other than English, facts show there are a good number of research publications in Spanish, Portuguese, Chinese, Russian, Turkish, German, French, and Korean that cannot be neglected. Considering the following results, we have to include languages other than English for our research query to perform bibliometric analysis. WoS provides a built-in feature to classify papers based upon the languages with respect to the particular research query.

Collaboration Network amongst Countries
The frequency of collaboration varies widely according to the scientific topic and discipline. Collaboration is very crucial for quality and timely research study in any field [23]. We used VOSviewer to conduct our study survey because it allows us to examine collaborative networks between countries. The circular elements (referred to as nodes) in VOSviewer represent a unit of analysis, and lines between nodes indicate that the respective two nodes collaborated on a research study. The weight of nodes is reflected in the size of the nodes. The weight of a node increases as its size increases. Greater weights, in this situation, indicate more collaboration for that specific country. Countries associated with each other very closely in terms of research studies belong to the same cluster and result in the formation of multiple co-authored research documents. Research Associativity is not only limited to intra-cluster collaboration, but is also extended to inter-cluster collaboration. However, the intra-cluster constitutes the countries collaborating with each other in a much more frequent manner.    The results also state that collaboration plays a vital role in enhancing countries' research outputs. Two of the most prominent countries from publications have the largest collaboration networks. These collaborations pave way for conducting timely research. Countries belonging to one cluster tend to collaborate more frequently than those belonging to other clusters

Correlation of Documents on the Basis of Co-Words
Co-word analysis is the method that is used to see the pattern of co-occurrence of keywords in a dataset [35]. Co-word analysis signifies the connections between the articles The results also state that collaboration plays a vital role in enhancing countries' research outputs. Two of the most prominent countries from publications have the largest collaboration networks. These collaborations pave way for conducting timely research. Countries belonging to one cluster tend to collaborate more frequently than those belonging to other clusters

Correlation of Documents on the Basis of Co-Words
Co-word analysis is the method that is used to see the pattern of co-occurrence of keywords in a dataset [35]. Co-word analysis signifies the connections between the articles based on the occurrence of the keyword [23]. Figures 12 and 14 represent word clouds using bibliometrix (Studio R) comprising the top 50 most common keywords for the years 2016-2018 and 2019-2021 respectively. However, from the visibility point of view, only the top 20 keywords are used for co-word analysis in the form of network visualization by using VOSViewer as shown in Figures 13 and 15 for the years 2016-2018 and 2019-2021, respectively. We have used the full counting method to create a keywords co-occurrence map. Keywords in the same cluster allude to themes that are similar or connected. In the evaluation of the top 20 keywords, the total link for all keywords is 19, indicating that each keyword is related to every other keyword. Each item has a link that indicates the co-occurrence of two words. The total number of times each keyword appears in each of the three clusters is displayed in Tables 15 and 16. We have used the full counting method to create a keywords co-occurrence map. Keywords in the same cluster allude to themes that are similar or connected.
In the evaluation of the top 20 keywords, the total link for all keywords is 19, indicating that each keyword is related to every other keyword. Each item has a link that indicates the co-occurrence of two words. The total number of times each keyword appears in each of the three clusters is displayed in Tables 15 and 16.           All the co-words that are more frequently used with one another are presented in one cluster. These clusters provide a ground for the identification of research themes/topics. For cluster 1, the word with highest number of occurrences for the time spans 2016-2018 is "model" and for 2019-2021 is "performance". For cluster 2, the term "software" is the most common terminology for both the time spans. Cluster 3 shows that for the time frame 2016-2018, the term which has the highest occurrences is "management" and for the time duration 2019-2021 it is "impact". Tables 15 and 16 depict that the keywords which belong to cluster 1 generally have a greater number of occurrences as compared to the other two clusters. Furthermore, it also highlights the fact that any software that is being developed or is under development is incomplete without Software Testing as the keyword "Software" has the highest weight (Figures 13 and 15) and the number of occurrences (Tables 15 and 16) in the publications related to the field of ST.

Research Themes/Topics
Using co-occurrence networks or co-word assessment, conceptual structure elucidates the connections among themes, subjects, and trends. It is the only approach that makes use of actual research findings. As a result, a study unit is a concept, term, or subject discovered in the network as a whole. To perform this analysis, we have used bibliometrix (R studio).
A two-dimensional diagram known as a "thematic map" depicts typological patterns [36]. The co-word analysis identifies keyword clusters, which in turn generate themes for research topics as shown in Figures 16 and 17 for the years (2016-2018) and (2019-2021) respectively. These themes can be divided into four quadrants on a two-dimensional graph on the basis of their density and centrality, which are the two dimensions of the graph. A bubble represents a theme on the map. including the first quarter (top right area): motor themes, a significant research concept that is getting momentum; The second quarter (top left area) contains highly evolved and isolated elements that have been well developed but are currently niche research issues; emerging theme in the third quarter (bottom left area): contains a study topic that has recently emerged or is on the verge of disappearing. The fourth quarter (bottom right side) contains the following information: basic elements, which are critical to the area, have not been extensively developed and often allude to major research topics [37]. Correspondence Analysis (CA) is a multivariate graphical tool that is used to investigate correlations between category data as shown in Figures 18 and 19 for the two respective timelines In this data, the red and blue clusters are shown in Figures 18 and 19. Words that are related to one another are found in each cluster. The red areas in the images (Figures 18 and 19) reveal a greater number of different terms that are related to each other. This demonstrates that many research publications are linked based on the words given in these clusters.
Topic dendrograms (Figures 20 and 21) depict the most commonly used topics, their relationships with other topics, and the classification of these topics in various colors. The majority of the topics come under a single cluster due to frequent relatedness amongst them which is shown by the red color in Figures 20 and 21. This also demonstrates that the themes in the blue classification have little in common with those in the red classification. Each of them is then split into many groups, each group into many sub-groups, and so on till the topic is used, at which point numerous topics are included in one group, showing a connection between the two topics in research publications in the field of Software Testing.

Research Themes/Topics
Using co-occurrence networks or co-word assessment, conceptual structure elucidates the connections among themes, subjects, and trends. It is the only approach that makes use of actual research findings. As a result, a study unit is a concept, term, or subject discovered in the network as a whole. To perform this analysis, we have used bibliometrix (R studio).
A two-dimensional diagram known as a "thematic map" depicts typological patterns [36]. The co-word analysis identifies keyword clusters, which in turn generate themes for research topics as shown in Figures 16 and 17 for the years (2016-2018) and (2019-2021) respectively. These themes can be divided into four quadrants on a two-dimensional graph on the basis of their density and centrality, which are the two dimensions of the graph. A bubble represents a theme on the map. including the first quarter (top right area): motor themes, a significant research concept that is getting momentum; The second quarter (top left area) contains highly evolved and isolated elements that have been well developed but are currently niche research issues; emerging theme in the third quarter (bottom left area): contains a study topic that has recently emerged or is on the verge of disappearing. The fourth quarter (bottom right side) contains the following information: basic elements, which are critical to the area, have not been extensively developed and often allude to major research topics [37]. Correspondence Analysis (CA) is a multivariate graphical tool that is used to investigate correlations between category data as shown in

Future Work
In future research, we intend to include databases such as Scopus, PubMed, and others besides the Web of Science. Moreover, in the future, we tend to perform detailed analyses on authors with respect to Software Testing. Analysis of various aspects of bibliometric assessment with respect to citations is out of the scope of this article but is intended to be carried out in the future. Although our research study itself is quite comprehensive, more search questions to uncover other bibliometric aspects of Software Testing would be covered in the future. Engineering that need to be analyzed in future works.

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Use of ISI Web of Science (WoS): We have used one of the most commonly used and highly privileged databases, which is ISI Web of Science. Other databases can also be used.

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Twelve research questions: Analysis on the basis of 12 research questions can be enhanced to include other bibliometric assessment parameters.

Conclusions
In this research paper, we have analyzed 75,098 publications from 2016 to 2021 in accordance with twelve research questions. Our research study represents the variation over two distinguished time frames (2016-2018 and 2019-2021) in different aspects of bibliometric assessment for Software Testing. Our findings suggest that the influence of Software Testing is not only limited to the Engineering and Computer Science field but spans multidisciplinary areas such as Medicine, Energy, Physics, Chemistry, and Environmental Sciences. The research publication trend shows an upward result from 2016-2019, where the year 2019 has the maximum number of publications. One of the possible reasons for the decline in the publication count for the years 2020 and 2021 could be the side effects of COVID-19.
The analysis of the top 20 institutions/organizations reveals that 35% of these institutions/organizations belong to the USA for the time frame 2016-2018, but this number is reduced to 30% for the time span 2019-2021. The rise in the number of Asian institutes/organizations is also observed when the two time frames are compared. For the years 2016-2018, the number of Asian institutes/organizations which are part of the leading 20 research institutions/organizations in terms of publications is six, but it has increased to seven for the years 2019-2021.
The USA and China have emerged as the top two leading countries from a research perspective for both the time frames. The record count of the published scholarly works has also increased from approximately 34.81% to approximately 38.47% for Asian countries with respect to the top 20 countries. However, Asia on the whole is the leading research contributor based on the publication count for the time frame (2019-2021).
Collaboration among the countries affirms the fact that a larger collaboration network plays a role in timely research production. USA and China are the two countries that have larger collaboration networks based on co-authored documents. Moreover, the clusters of collaboration networks state that although countries belonging to the same cluster frequently collaborate with each other, both inter-cluster and intra-cluster collaboration is carried out. The findings of the publication medium state that although English has a major contribution as the medium of the published articles, qualitative articles are also published in languages other than the English language.
Co-word occurrence plays a vital role in not only depicting the relatedness amongst documents, but also forming the basis of various thematic analyses as shown in our study. The keyword "Software" has the greatest number of occurrences which shows that Software Testing plays a vital role in the development of Software. The topic dendrogram specifically represents the hierarchical relationship that exists amongst various themes.
The top 20 most relevant sources represent the 20 most contributing publication venues in terms of publication count. This factor further highlights the fact that Software Testing is a field that has impact and uses in other multi-disciplinary areas.
We can conclude that to the best of our knowledge, our comprehensive research study in the Software Testing domain is the first one of its kind.
Future research plans include incorporating databases like Scopus, PubMed, and others, not just Web of Science. Software testing will be analyzed in greater detail in the future, as well. Out of the scope of this article, but planned for the future, is an investigation into bibliometric assessment of citations.