  Combinatorial Testing (CT) is a potentially powerful testing technique,
whereas its failure revealing ability might be dramatically reduced if it fails
to handle constraints in an adequate and efficient manner. To ensure the wider
applicability of CT in the presence of constrained problem domains, large and
diverse efforts have been invested towards the techniques and applications of
constrained combinatorial testing. In this paper, we provide a comprehensive
survey of representations, influences, and techniques that pertain to
constraints in CT, covering 129 papers published between 1987 and 2018. This
survey not only categorises the various constraint handling techniques, but
also reviews comparatively less well-studied, yet potentially important,
constraint identification and maintenance techniques. Since real-world programs
are usually constrained, this survey can be of interest to researchers and
practitioners who are looking to use and study constrained combinatorial
testing techniques.
