Assessing Diffusion and Perception of Test Smells in Scala Projects

Test smells are, analogously to code smells, defined as the characteristics exhibited by poorly designed unit tests. Their negative impact on test effectiveness, understanding, and maintenance has been demonstrated by several empirical studies. However, the scope of these studies has been limited mostly to Java in combination with the JUnit testing framework. Results for other language and framework combinations are --despite their prevalence in practice-- few and far between, which might skew our understanding of test smells. The combination of Scala and ScalaTest, for instance, offers more comprehensive means for defining and reusing test fixtures, thereby possibly reducing the diffusion and perception of fixture-related test smells. This paper therefore reports on two empirical studies conducted for this combination. In the first study, we analyse the tests of 164 open-source Scala projects hosted on GitHub for the diffusion of test smells. This required the transposition of their original definition to this new context, and the implementation of a tool (SOCRATES) for their automated detection. In the second study, we assess the perception and the ability of 14 Scala developers to identify test smells. For this context, our results show (i) that test smells have a low diffusion across test classes, (ii) that the most frequently occurring test smells are LazyTest, EagerTest, and AssertionRoulette, and (iii) that many developers were able to perceive but not to identify the smells.