How to build gtest tests in ros2?

edit

I am trying to build tests with ros2, but I'm getting linker errors with gtest.

I guess my question is: "Why am I getting linking errors with gtest?"

This is my CMake:

cmake_minimum_required(VERSION 3.5)
project(bluebotics_ant)

find_package(ament_cmake REQUIRED)
find_package(ethernetip_interface REQUIRED)
find_package(cpp_threading_helpers REQUIRED)
find_package(rclcpp REQUIRED)
find_package(ament_index_cpp REQUIRED)
find_package(ament_cmake_gtest REQUIRED)
find_package(builtin_interfaces REQUIRED)
find_package(rosidl_default_generators REQUIRED)
find_package(std_msgs REQUIRED)

find_package(Boost 1.47 REQUIRED COMPONENTS system)

rosidl_generate_interfaces(${PROJECT_NAME}
        # messages
        "msg/ANTInfo.msg"
        # actions
        # "action/example.action"
        DEPENDENCIES builtin_interfaces)

set(${PROJECT_NAME}_SRCS
        src/ant_node.cpp
        src/ant_driver.cpp
        src/ant_generic_data_assembly.cpp
        src/plc_generic_data_assembly.cpp
        test/assembly_time_values_test.cpp
        src/ant_kinematics_assembly.cpp)

add_executable(ant_test src/main.cpp ${${PROJECT_NAME}_SRCS})
target_include_directories(ant_test
        PUBLIC
        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
        $<INSTALL_INTERFACE:include>
        )
ament_target_dependencies(
        ant_test
        rclcpp
        ethernetip_interface
        cpp_threading_helpers
        ament_index_cpp
)
rosidl_target_interfaces(ant_test
        ${PROJECT_NAME} "rosidl_typesupport_cpp")

install(TARGETS
        ant_test
        DESTINATION lib/${PROJECT_NAME}
        )

# Install EtherNet/IP ANT device config as symlink
INSTALL(CODE "execute_process( \
    COMMAND ${CMAKE_COMMAND} -E create_symlink \
    ${CMAKE_SOURCE_DIR}/config/data.yaml \
    ${CMAKE_INSTALL_PREFIX}/share/data.yaml \
    )"
        )
# Install EtherNet/IP ANT device kinematics config as symlink
INSTALL(CODE "execute_process( \
    COMMAND ${CMAKE_COMMAND} -E create_symlink \
    ${CMAKE_SOURCE_DIR}/config/tricycle_kinematics.yaml \
    ${CMAKE_INSTALL_PREFIX}/share/tricycle_kinematics.yaml \
    )"
        )

if (BUILD_TESTING)
    find_package(ament_lint_auto REQUIRED)
    ament_lint_auto_find_test_dependencies()
    ament_add_gtest(${PROJECT_NAME}_test test/assembly_time_values_test.cpp ${${PROJECT_NAME}_SRCS})
    target_include_directories(${PROJECT_NAME}_test
            PUBLIC
            $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
            $<INSTALL_INTERFACE:include>
            )
    ament_target_dependencies(
            ${PROJECT_NAME}_test
            rclcpp
            ethernetip_interface
            cpp_threading_helpers
            ament_index_cpp
    )
    rosidl_target_interfaces(${PROJECT_NAME}_test
            ${PROJECT_NAME} "rosidl_typesupport_cpp")
endif ()

ament_package()

This is the console output when building:

Starting >>> cpp_threading_helpers
Starting >>> odva_ethernetip
Finished <<< cpp_threading_helpers [4.05s]                                                                    
Starting >>> meta_cpp_helpers
Finished <<< meta_cpp_helpers [1.59s]                                                                 
Finished <<< odva_ethernetip [14.4s]                       
Starting >>> ethernetip_interface
Finished <<< ethernetip_interface [5.03s]                     
Starting >>> bluebotics_ant
--- stderr: bluebotics_ant                                
/usr/bin/ld: CMakeFiles/ant_test.dir/test/assembly_time_values_test.cpp.o: in function `bluebotics_ant::tests::AssemblyTimeValuesTest_WriteReadPLCTime_Test::TestBody()':
assembly_time_values_test.cpp:(.text+0x3bf): undefined reference to `testing::Message::Message()'
/usr/bin/ld: assembly_time_values_test.cpp:(.text+0x3f4): undefined reference to `testing::internal::AssertHelper::AssertHelper(testing::TestPartResult::Type, char const*, int, char const*)'
/usr/bin/ld: assembly_time_values_test.cpp:(.text+0x40d): undefined reference to `testing::internal::AssertHelper::operator=(testing::Message const&) const'
/usr/bin/ld: assembly_time_values_test.cpp:(.text+0x41c): undefined reference to `testing::internal::AssertHelper::~AssertHelper()'
/usr/bin/ld: assembly_time_values_test.cpp:(.text+0x4ec): undefined reference to `testing::internal::AssertHelper::~AssertHelper()'
/usr/bin/ld: CMakeFiles/ant_test.dir/test/assembly_time_values_test.cpp.o: in function `bluebotics_ant::tests::main(int, char**)':
assembly_time_values_test.cpp:(.text+0x59b): undefined reference to `testing::InitGoogleTest(int*, char**)'
...