Design Con 2015

The relationship between software assertions and code quality

Gunnar Kudrjavets, Microsoft Corp. and Nachiappan Nagappan and Thomas Ball, Microsoft Research

June 10, 2013

Gunnar Kudrjavets, Microsoft Corp. and Nachiappan Nagappan and Thomas Ball, Microsoft ResearchJune 10, 2013

The use of assertions in software development is thought to help produce quality software. Unfortunately, there is scant empirical evidence in commercial software systems for this argument to date.

This paper presents an empirical case study of two commercial software components at Microsoft Corporation. The developers of these components systematically employed assertions, which allowed us to investigate the relationship between software assertions and code quality.

There have been several research papers on the formal analysis of assertions in code, their utility in contracts, investigations on the placement of assertions etc. but none on the practical implications of using assertions in commercial code bases. This paper attempts to address this question from an empirical perspective.

We also compare the efficacy of assertions against that of popular bug finding techniques like source code static analysis tools. We observe from our case study that with an increase in the assertion density in a file there is a statistically significant decrease in fault density. Further, the usage of software assertions in these components found a large percentage of the faults in the bug database.

Based on talking to different developers and managers across Microsoft our observation is that unless there is a culture of using assertions, such mandates will not produce the desired results.

If the developers are mature enough to understand the code base and write useful assertions, it is highly likely that they understand the code base, which will lead to a lower fault density. We feel there is an urgent need in educating students about the utility of software assertions.

To read this external content in full, download the paper from the Microsoft Research technical article archives.


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