Automated unit test generation consists of two complementary challenges: Finding sequences of API calls that exercise the code of a class under test, and finding assertion statements that validate the behavior of the class during execution. The former challenge is often addressed using meta-heuristic search algorithms optimising tests for code coverage, which are then annotated with regression assertions to address the latter challenge, i.e., assertions that capture the states observed during test generation. While the resulting tests tend to achieve high coverage, their fault finding potential is often inhibited by poor or difficult observability of the codebase. That is, relevant attributes and properties may either not be exposed adequately at all, or only in ways that the test generator is unable to handle. In this paper, we investigate the influence of observability in the context of the EvoSuite search-based Java test generator, which we extend in two complementary ways to study and improve observability: First, we apply a transformation to code under test to expose encapsulated attributes to the test generator; second, we address EvoSuite's limited capability of asserting the state of complex objects. Our evaluation demonstrates that together these observability improvements lead to significantly increased mutation scores, underscoring the importance of considering the class observability in the test generation process.

Diverse studies have analyzed the quality of automatically generated test cases by using test smells as the main quality attribute. But recent work reported that generated tests might suffer from a number of quality issues not considered previously, thus suggesting that not all test smells have been identified yet. Little is known about these issues and their frequency within generated tests. In this paper, we report on a manual analysis of an external dataset consisting of 2,340 automatically generated tests. This analysis aimed at detecting new quality issues, not covered by past recognized test smells. We use thematic analysis to group and categorize the new quality issues found. As a result, we propose a taxonomy of 13 new quality issues grouped in four categories. We also report on the frequency of these new quality issues within the dataset and present eight recommendations that test generators may consider to improve the quality and usefulness of the automatically generated tests. As an additional contribution, our results suggest that (i) test quality should be evaluated not only on the tests themselves, but considering also the tested code; and (ii) automatically generated tests present flaws that are unlikely to be found in manually created tests and thus require specific quality checking tools.