It's a port of Google Testing framework to IBM System i aka (os/400) aka (AS/400) aka (i5/OS). If, or while this changes won't be included in mainstream source tree, you can obtain Google Tests porting for os/400 | IBM System i there.
It can be fully compiled via CRTCPPMOD.
Your gtest-1.6.0 bundle must be putted on system i as a set of stream files.
Just run for compile module:
CRTCPPMOD SRCSTMF('<gtest-path>/src/gtest-all.cc') INCDIR('<gtest-path>/include''<gtest-path>')
Then this module can be linked to any ILE programm via CRTPGM.