fatal error: gtest/gtest.h: No such file or directory

[To-be-or-not]

Hi all,
When I build and make the file. There is a problem like
$ make Scanning dependencies of target easyloggingpp-unit-tests [ 33%] Building CXX object CMakeFiles/easyloggingpp-unit-tests.dir/src/easylogging++.cc.o [ 66%] Building CXX object CMakeFiles/easyloggingpp-unit-tests.dir/test/main.cc.o In file included from /afs/cern.ch/work/w/wangxi/public/SS_3L/strong/easyloggingpp/test/main.cc:3: /afs/cern.ch/work/w/wangxi/public/SS_3L/strong/easyloggingpp/test/test.h:11:10: fatal error: gtest/gtest.h: No such file or directory #include <gtest/gtest.h>

Do you have any experience abou this? Any comments are welcome!