Here is a proposed patch which lengths the GTest discover timeout:
http://review.source.kitware.com/#/c/23608/
The DISCOVERY_TIMEOUT option was added in CMake 3.10, perhaps the default of 5 seconds is too short:
https://cmake.org/cmake/help/v3.10/module/GoogleTest.html
There is a compatibility issue with CMake 3.10.2:
In CMake versions 3.10.1 and 3.10.2, this option was called TIMEOUT. This clashed with the TIMEOUT test property, which is one of the common properties that would be set with the PROPERTIES keyword, usually leading to legal but unintended behavior. The keyword was changed to DISCOVERY_TIMEOUT in CMake 3.10.3 to address this problem. The ambiguous behavior of the TIMEOUT keyword in 3.10.1 and 3.10.2 has not been preserved.
I guess we are stuck with 3.10.2.