How the Experience of Development Teams Relates to Assertion Density of Test Classes

The impact of developers' experience on several development practices has been widely investigated in the past. One of the most promising research fields is software testing, as many researchers found significant correlations between developers' experience and testing effectiveness. In this paper, we aim at further studying this relation, by focusing on how development teams' experience is associated with the assertion density, i.e., the number of assertions per test class KLOC, that has previously been shown as an effective way to decrease fault density. We perform a mixed-methods empirical study. First, we devise a statistical model relating development teams' experience and other control factors to the assertion density of test classes belonging to 12 software projects. This model enables us to investigate whether experience comes out as a statistically significant factor to explain assertion density. Second, we contrast the statistical findings with a survey study conducted with 57 developers, who were asked their opinions on how developer's experience is related to the way they add assertions in test code. Our findings suggest the existence of a relationship: On the one hand, the development team's experience is a statistically significant factor in most of the systems that we have investigated; on the other hand, developers confirm the importance of experience and team composition for the effective testing of production code.