  Requirements Engineering and Software Testing are mature areas and have seen
a lot of research. Nevertheless, their interactions have been sparsely explored
beyond the concept of traceability. To fill this gap, we propose a definition
of requirements engineering and software test (REST) alignment, a taxonomy that
characterizes the methods linking the respective areas, and a process to assess
alignment. The taxonomy can support researchers to identify new opportunities
for investigation, as well as practitioners to compare alignment methods and
evaluate alignment, or lack thereof. We constructed the REST taxonomy by
analyzing alignment methods published in literature, iteratively validating the
emerging dimensions. The resulting concept of an information dyad characterizes
the exchange of information required for any alignment to take place. We
demonstrate use of the taxonomy by applying it on five in-depth cases and
illustrate angles of analysis on a set of thirteen alignment methods. In
addition, we developed an assessment framework (REST-bench), applied it in an
industrial assessment, and showed that it, with a low effort, can identify
opportunities to improve REST alignment. Although we expect that the taxonomy
can be further refined, we believe that the information dyad is a valid and
useful construct to understand alignment.
