Heterogeneous systems comprising sets of inherent subsystems are challenging to integrate. In particular, testing for interoperability and conformance is a challenge. Furthermore, the complexities of such systems amplify traditional testing challenges. We explore (1) which techniques are frequently discussed in literature in context of heterogeneous system testing that practitioners use to test their heterogeneous systems; (2) the perception of the practitioners on the usefulness of the techniques with respect to a defined set of outcome variables. For that, we conducted an exploratory survey. A total of 27 complete survey answers have been received. Search-based testing has been used by 14 out of 27 respondents, indicating the practical relevance of the approach for testing heterogeneous systems, which itself is relatively new and has only recently been studied extensively. The most frequently used technique is exploratory manual testing, followed by combinatorial testing. With respect to the perceived performance of the testing techniques, the practitioners were undecided regarding many of the studied variables. Manual exploratory testing received very positive ratings across outcome variables.