  For software to be reliable and resilient, it is widely accepted that tests
must be created and maintained alongside the software itself. One safeguard
from vulnerabilities and failures in code is to ensure correct behavior on the
boundaries between the input space sub-domains. So-called boundary value
analysis (BVA) and boundary value testing (BVT) techniques aim to exercise
those boundaries and increase test effectiveness. However, the concepts of BVA
and BVT themselves are not generally well defined, and it is not clear how to
identify relevant sub-domains, and thus the boundaries delineating them, given
a specification. This has limited adoption and hindered automation. We clarify
BVA and BVT and introduce Boundary Value Exploration (BVE) to describe
techniques that support them by helping to detect and identify boundary inputs.
Additionally, we propose two concrete BVE techniques based on
information-theoretic distance functions: (i) an algorithm for boundary
detection and (ii) the usage of software visualization to explore the behavior
of the software under test and identify its boundary behavior. As an initial
evaluation, we apply these techniques on a much used and well-tested date
handling library. Our results reveal questionable behavior at boundaries
highlighted by our techniques. In conclusion, we argue that the boundary value
exploration that our techniques enable is a step towards automated boundary
value analysis and testing, fostering their wider use and improving test
effectiveness and efficiency.
