International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015 1285

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An Empirical Study on Testability

Measurement of Object Oriented Software

M.A. Khanum1, Arun Mani Tripathi2
Associate Professor, Department of Computer Application , Integral University, Lucknow,India 1
M.tech student, C.S.E., Integral University, Lucknow, 2

Abstract: Testability has always been a difficult exercise and its accurate estimation or assessment a complex exercise. Most of the studies quantify testability or more specifically the attributes that have influence on software testability but at the implementation level. A decision to transform the design in order to improve software testability after implementation has started may be very error prone and expensive. While estimating testability early in the software development life cycle may significantly reduce the overall development cost. In this paper Testability has been recognized as a major factor to object oriented software quality and importance is being drawn to measure design testability, near the beginning in the software development process. Study identified effectiveness and flexibility are the major factors that affect overall testability at design phase. The identified testability factors are to be correlated with the object oriented design characteristics. After successfully establishing the relationship, study developed Testability Measurement Model for Object Oriented Design. Subsequently testability model has been empirically validated and contextual interpretation has been performed using try out software projects.

Keywords: Testability, Flexibility, Effectiveness, Testability Model

I. INTRODUCTION
Software systems are fastest emerging trend in the real world and the probable possibilities concerning the functions and features provided by a precise application is generating remarkable interest amongst a huge number of users around the world [1-3]. As the importance grows, so does the request for software application. In view of the fact that development of large software system involves a number of activities which are need to be properly coordinated to fulfill expected requirements [4][5]. Therefore in current scenario the importance for developing good quality software is not longer an advantage but an essential factor. Software testing is one the most fundamental method to correct the system faults and also help in improving the software quality directly [6].
Assessment of software product quality throughout the development life cycle is very important to manage and improve the software quality [7-10]. Assessment of software quality after the completion of development work is no longer an advantage but it is more important to monitor and manage the quality of software when it is under development [11][12]. Thus, there is a need for identifying the design properties, which may be used in early stage of development to give good indication of software quality [13]. In order to provide the significant assessment of software product quality, it is important to identify a set of high-level desirable quality attributes, and to find a way to relate the design properties to quality attributes, significantly. In this regard an effort has been made in this paper.
II. SOFTWARE TESTABILITY
The common definition of testability is ease of performing testing. Object oriented design testability is an
external quality attribute that estimates the complexity and the required effort for software testing. Software testability is a main aspect to permit the detection of difficulties to uncover defects in software. The IEEE Standard Glossary defines testability as the degree to which a system or component facilitates the establishment of test criteria and performance of tests to determine whether those criteria have been met [14][16].Software testability is a non- functional requirements and important to the testing team member, who are involved in user acceptance testing. Non functional requirements are generally a quality requirement and may make the user more satisfied and pleased[15]. Testability is one of the significant concept in software design and testing software program and its components. Creating programs and components with greater level testability constantly simplify the test process; reduce cost, and increases software quality [17].

III. FACTOR IDENTIFICATION

Software testability is a major factor to software quality. In order to estimate testability, its direct measures are to be recognized [18][19]. In this study, the commonly accepted group of factors for testability are identified. Object oriented design level factors will also be examined keeping in view their overall impact on the software testability. Most of the mechanisms available for testability estimation of object oriented software, may normally be used in later phases of system development life cycle and rely upon information extracted on the operationalization of software [20]. Such methods provide an indication of testability and hence quality, but too late to improve the product, prior to its completion. The characteristics of testable software like adequate complexity, low coupling and good separation of concerns make it easier for reviewers to understand the software artifacts under review [21][23]. Plenty of work has been carried out in describing the need and importance of

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incorporating software testability since early 90s. A number of methods of measuring testability have been proposed[24]. Unfortunately, the significant achievements made by the researchers in the area have not been widely accepted and are not adopted in practice by industry [22]. It has been found that there is a conflict in considering the factors while estimating software testability in general and at design level exclusively.

IV. SOFTWARE CHARACTERIZATION

In this section study will be identified different design characteristics that have their impacts on software testability measurement and product quality as well. The involvement of each properties help to improve the software design will also be analyzed. The consolidated charting for the object oriented design properties considered by different researchers is shown in following table. This study shows that abstraction is least important factor in while cohesion, coupling, encapsulation and inheritance play key role in testability measurement.

V. CORRELATION ESTABLISHMENT

Correlation establishment is an important step between testability and its major identified factors. In this step the recognized software testability factors are to be correlated with the Object Oriented design properties. A regression line will be established to quantify testability factors in
terms of design characteristics with the help of design
metrics. Here ENM shows encapsulation metrics, INM shows inheritance metrics, CPM shows cohesion metrics and COM shows coupling metrics value in following figure.

Fig. 1. Correlation Establishment
VI. MODEL DEVELOPMENT
Quantification of design diagram Effectiveness and Functionality is precondition for the testability estimation model. For that reason before developing testability model, the research paper has developed 2 models for
Effectiveness and Functionality. In order to develop all the models given below multivariate linear model is applied.
Y=µ + β1 *X1 + β2 *X2 +…….+ βn *Xn +ε (1)

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VI .A) FLEXIBILITY ESTIMATION MODEL

Flexibility is strongly related to testability and regularly plays a key role to deliver high class, best quality testable
software within time and given budget [6] [19]. It is one of the most important notions in design for testing of software programs and components [11][12].

Flexibility= -2.004 + .029 × Coupling + 14.091 × Inheritance + 3.964 × Encapsulation (2)

VI. B) EFFECTIVENESS ESTIMATION MODEL

Effectiveness is strongly related to testability and regularly plays a key role to deliver high class, best quality
testable software within time and given budget [13] [15]. It is one of the most important notions in design for testing of software programs and components [11][17].

Effectiveness = - 9.440 - 4.161× Encapsulation +1.506 × Coupling + 26.392 × Cohesion (3)

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VII. TESTABILITY ESTIMATION MODEL

The generic quality models [12] [16][19] have been considered as a basis to develop the Testability Model.Before developing the model for Testability, it is important to make sure the appropriate association among Testability, Flexibility and Effectiveness of class
diagrams. Table below, shows the relationship values among them. From the correlation values it is clear that both Flexibility and Effectiveness are strongly correlated with Testability.

TABLE IX Coefficientsa
Unstandardized Coefficients Standardized

a. Dependent Variable: testability

Testability= 4.227+.260× Flexibility+.534 ×Effectiveness (4)

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VIII. EMPIRICAL VALIDATION OF DEVELOPED

MODEL

Empirical validation is a vital phase of proposed research. Empirical validation is the standard approach to justify the model approval. Taking view of this truth, practical validation of the Testability model has been
performed using sample tryouts. In order to validate developed Testability model the data has been taken from [11].
TABLE XII : COMPUTED RANKING, ACTUAL RANKING AND THEIR RELATION
Testability Ranking
Projects



P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
Computed Rank
A l R k
∑d2 rs r s> ±.781
25
• rs above±.781 means significant results. Speraman’s Coefficient of Correlation rs was used to
check the significance of correlation among calculated
values of testability using model and it’s ‘Known Values’. The ‘rs ’ was estimated using the method given as under: Speraman’s Coefficient[1] of Correlation

‘d’ = difference between ‘Calculated ranking’ and
‘Known ranking’ of testability.
‘n' = number of projects (n=10) used in the experiment. The correlation values between testability through model and known ranking are shown in table XII. Pairs of these values with correlation values rs above [±.781] are checked in table. The correlations are up to standard with high degree of confidence, i.e. up to 99%. Therefore we can conclude without any loss of generality that testability Estimation model measures are really reliable and
significant and applicable.
IX. CONCLUSION
The model developed in the paper will address testability at design stage of software development life cycle. It may also help to positioning testability benchmarking of software projects. From the correlation

values it is clear that both Flexibility and Effectiveness are strongly correlated with testability. It plays a significant role as far as the issues of delivering quality software are
concerned. Therefore, the software testability model has been validated theoretically as well as mathematically using experimental try-out. Outcome result shows that the values of software testability computed through model are highly correlated with the ‘known values’. The applied validation on the testability estimation model concludes that developed model is highly consistent, acceptable and reliable. The model is developed, may be used by software industry practitioners and quality controllers to measure testability in order to make good design decisions near the beginning in the software development life cycle.

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