Effects of Test-Driven Development : A Comparative Analysis of Empirical Studies

Test-driven development is a software development practice where small sections of test code are used to direct the development of program units. Writing test code prior to the production code promises several positive effects on the development process itself and on associated products and processes as well. However, there are few comparative studies on the effects of test-driven development. Thus, it is difficult to assess the potential process and product effects when applying test-driven development. In order to get an overview of the observed effects of test-driven development, an in-depth review of existing empirical studies was carried out. The results for ten different internal and external quality attributes indicate that test-driven development can reduce the amount of introduced defects and lead to more maintainable code. Parts of the implemented code may also be somewhat smaller in size and complexity. While maintenance of test-driven code can take less time, initial development may last longer. Besides the comparative analysis, this article sketches related work and gives an outlook on future research.Peer reviewe

Empirical Investigation on Agile Methods Usage: Issues Identified from Early Adopters in Malaysia

Agile Methods are a set of software practices that can help to produce products faster and at the same time deliver what customers want. Despite the benefits that Agile methods can deliver, however, we found few studies from the Southeast Asia region, particularly Malaysia. As a result, less empirical evidence can be obtained in the country making its implementation harder. To use a new method, experience from other practitioners is critical, which describes what is important, what is possible and what is not possible concerning Agile. We conducted a qualitative study to understand the issues faced by early adopters in Malaysia where Agile methods are still relatively new. The initial study involves 13 participants including project managers, CEOs, founders and software developers from seven organisations. Our study has shown that social and human aspects are important when using Agile methods. While technical aspects have always been considered to exist in software development, we found these factors to be less important when using Agile methods. The results obtained can serve as guidelines to practitioners in the country and the neighbouring regions

Software defect prediction: do different classifiers find the same defects?

Open Access: This article is distributed under the terms of the Creative Commons Attribution 4.0 International License CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.During the last 10 years, hundreds of different defect prediction models have been published. The performance of the classifiers used in these models is reported to be similar with models rarely performing above the predictive performance ceiling of about 80% recall. We investigate the individual defects that four classifiers predict and analyse the level of prediction uncertainty produced by these classifiers. We perform a sensitivity analysis to compare the performance of Random Forest, Naïve Bayes, RPart and SVM classifiers when predicting defects in NASA, open source and commercial datasets. The defect predictions that each classifier makes is captured in a confusion matrix and the prediction uncertainty of each classifier is compared. Despite similar predictive performance values for these four classifiers, each detects different sets of defects. Some classifiers are more consistent in predicting defects than others. Our results confirm that a unique subset of defects can be detected by specific classifiers. However, while some classifiers are consistent in the predictions they make, other classifiers vary in their predictions. Given our results, we conclude that classifier ensembles with decision-making strategies not based on majority voting are likely to perform best in defect prediction.Peer reviewedFinal Published versio

Dynamics of railway freight vehicles

This paper summarises the historical development of railway freight vehicles and how vehicle designers have tackled the difficult challenges of producing running gear which can accommodate the very high tare to laden mass of typical freight wagons whilst maintaining stable running at the maximum required speed and good curving performance. The most common current freight bogies are described in detail and recent improvements in techniques used to simulate the dynamic behaviour of railway vehicles are summarised and examples of how these have been used to improve freight vehicle dynamic behaviour are included. A number of recent developments and innovative components and sub systems are outlined and finally two new developments are presented in more detail: the LEILA bogie and the SUSTRAIL bogie

Wpływ dodatku osadu dennego do gleby na plon i skład chemiczny kukurydzy

A two-year pot experiment was conducted to assess the effect of bottom sediment, used as a supplement to the light soil, on the yield and contents of macroelements in maize. The bottom sediment was added to light soil in the proportion of 5 and 10 %. The material was classified to a group of ordinary silt deposit. Moreover, the analyzed sediment revealed alkaline reaction, organic matter content of 25.8 g kg-1, low content of bioavailable phosphorus and potassium and natural content of heavy metals. After the experiment completion the amount of maize dry matter yield was assessed. The contents of minerals in the plant mass was determined after dry mineralization and the ash dissolving in HNO3 (1:3), K, Mg, Ca, and Na were determined using AAS and P with ICP-AES technique. Nitrogen content was determined by means of Kjeldahl distillation method. The experiment demonstrated a positive effect of bottom sediment supplement to light soil on the amount of produced maize biomass. The greatest maize biomass was obtained on the treatment with a 5 % admixture of bottom sediment. However, the plant shoot biomass did not meet the criteria for good quality fodder because of too low contents of most macroelements. It was found that the analyzed bottom sediment may be used as an admixture to light and acid soils to improve their productivity, owing to a considerable share of silt and clay fractions in its composition, neutral reaction and low content of heavy metals. However, each agricultural application of bottom sediment requires a supplementary mineral fertilization because of low contents of fertilizer elements in the sediment and in the obtained maize biomass.Celem dwuletniego doświadczenia wazonowego była ocena wpływu osadu dennego stosowanego jako dodatek do gleby lekkiej na plon i zawartość makrślementów w kukurydzy. Osad denny dodano do gleby lekkiej w ilości 5 i 10 %. Materiał ten zakwalifikowano do grupy utworów pyłowych zwykłych i charakteryzował się on odczynem zasadowym, zawartością materii organicznej wynoszącą 25,8 g kg-1, niską zawartością przyswajalnego fosforu i potasu oraz naturalną zawartością metali ciężkich. Po zakończeniu doświadczenia określono wielkość plonu suchej masy kukurydzy. Zawartość składników mineralnych w materiale roślinnym oznaczono po suchej mineralizacji i roztworzeniu popiołu w HNO3 (1:3), techniką AAS (K, Mg, Ca, Na) oraz ICP-EAS (P). Zawartość N oznaczono metodą destylacyjną Kjeldahla. Stwierdzono pozytywny wpływ osadu dennego dodanego do gleby lekkiej na plon biomasy kukurydzy. Największą biomasę rośliny uzyskano w obiekcie z dodatkiem osadu w ilości 5 %. Nadziemna biomasa roślinna nie spełniała jednak kryteriów dla paszy dobrej jakości, ze względu na zbyt małe zawartości większości makrślementów. Stwierdzono, że badany osad denny ze względu na duży udział frakcji pylastych i ilastych w swoim składzie, obojętny odczyn i małą zawartość metali ciężkich może być stasowany jako dodatek do gleb lekkich i kwaśnych w celu poprawy ich produkcyjności. W rolniczym wykorzystaniu osadu dennego należy jednak zastosować uzupełniające nawożenie mineralne z powodu niskiej zawartości pierwiastków nawozowych w osadzie oraz biomasie kukurydzy