  Recent efforts in practical symbolic execution have successfully mitigated
the path-explosion problem to some extent with search-based heuristics and
compositional approaches. Similarly, due to an increase in the performance of
cheap multi-core commodity computers, fuzzing as a viable method of random
mutation-based testing has also seen promise. However, the possibility of
combining symbolic execution and fuzzing, thereby providing an opportunity to
mitigate drawbacks in each other, has not been sufficiently explored. Fuzzing
could, for example, expedite path-exploration in symbolic execution, and
symbolic execution could make seed input generation in fuzzing more efficient.
There have only been, in our view, very few hybrid solution proposals with
symbolic execution and fuzzing at their centre. By analyzing 77 relevant and
systematically selected papers, we (1) present an overview of hybrid solution
proposals of symbolic execution and fuzzing, (2) perform a gap analysis in
research of hybrid techniques to improve both, plain symbolic execution and
fuzzing, (3) propose new ideas for hybrid test-case generation techniques.
