  Context: Search-based software testing promises to provide users with the
ability to generate high-quality test cases, and hence increase product
quality, with a minimal increase in the time and effort required. One result
that emerged out of a previous study to investigate the application of
search-based software testing (SBST) in an industrial setting was the
development of the Interactive Search-Based Software Testing (ISBST) system.
ISBST allows users to interact with the underlying SBST system, guiding the
search and assessing the results. An industrial evaluation indicated that the
ISBST system could find test cases that are not created by testers employing
manual techniques. The validity of the evaluation was threatened, however, by
the low number of participants.
  Objective: This paper presents a follow-up study, to provide a more rigorous
evaluation of the ISBST system.
  Method: To assess the ISBST system a two-way crossover controlled experiment
was conducted with 58 students taking a Verification and Validation course. The
NASA Task Load Index (NASA-TLX) is used to assess the workload experienced by
the participants in the experiment.
  Results: The experimental results validated the hypothesis that the ISBST
system generates test cases that are not found by the same participants
employing manual testing techniques. A follow-up laboratory experiment also
investigates the importance of interaction in obtaining the results. In
addition to this main result, the subjective workload was assessed for each
participant by means of the NASA-TLX tool. The evaluation showed that, while
the ISBST system required more effort from the participants, they achieved the
same performance.
  Conclusions: The paper provides evidence that the ISBST system develops test
cases that are not found by manual techniques, and that interaction plays an
important role in achieving that result.
