gtest not found

[candyguo]

platform: ubuntu16.04 , ros kinetic
I follow the guide of "how to install", when run " catkin build aerial_mapper", I meet following error,
hope to get some advice. Thanks!

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Errors << cv_bridge:cmake /home/ccfy/software/catkin_ws_aerial_mapper/logs/cv_bridge/build.cmake.015.log
CMake Warning at /opt/ros/kinetic/share/catkin/cmake/test/gtest.cmake:149 (message):
skipping gtest 'cv_bridge-utest' in project 'cv_bridge' because gtest was
not found
Call Stack (most recent call first):
/opt/ros/kinetic/share/catkin/cmake/test/gtest.cmake:79 (_catkin_add_executable_with_google_test)
/opt/ros/kinetic/share/catkin/cmake/test/gtest.cmake:28 (_catkin_add_google_test)
test/CMakeLists.txt:6 (catkin_add_gtest)

CMake Error at /home/ccfy/software/catkin_ws_aerial_mapper/src/vision_opencv/cv_bridge/test/CMakeLists.txt:7 (target_link_libraries):
Cannot specify link libraries for target "cv_bridge-utest" which is not
built by this project.

cd /home/ccfy/software/catkin_ws_aerial_mapper/build/cv_bridge; catkin build --get-env cv_bridge | catkin env -si /usr/bin/cmake /home/ccfy/software/catkin_ws_aerial_mapper/src/vision_opencv/cv_bridge --no-warn-unused-cli -DCATKIN_DEVEL_PREFIX=/home/ccfy/software/catkin_ws_aerial_mapper/devel -DCMAKE_INSTALL_PREFIX=/home/ccfy/software/catkin_ws_aerial_mapper/install -DCMAKE_BUILD_TYPE=Release; cd -
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Failed << cv_bridge:cmake [ Exited with code 1 ]
Failed <<< cv_bridge [ 1.8 seconds ]

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