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cmakegoogletestcatkin

Compile gtest from source with catkin

I am trying to compile gtest from source (instead of using the existing installed version). I am working on a catkin based cmake project.

I have added the sourcecode from https://github.com/google/googletest to my workspace and included the folder with add_subdirectory.

However, I get a nameclash with the existing gtest:

CMake Error at src/test_env/GTest/googletest/cmake/internal_utils.cmake:151 (add_library):
  add_library cannot create target "gtest" because another target with the
  same name already exists.  The existing target is a shared library created
  in source directory "/usr/src/gtest".  See documentation for policy CMP0002
  for more details.

From other posts, and the googletest instructions itself (https://github.com/google/googletest/tree/master/googletest#incorporating-into-an-existing-cmake-project) I understand that this should be no problem.

I think the problem might lie in how catkin handles gtest. And, admittedly, normally I could just use the installed version. But I want to make sure, that everyone uses the same (bundled) version of gtest.

Any suggestions and hints are welcomed.

Solution

  • Okay, so the error message is actually quite clear. A cmake "target" is "something that will be produced by the build", be it a library, or an executable, or something else. So, the problem is that you are trying to add a target named "gtest", and catkin already does the same thing. Both would produce the library "libgtest.so", and of course there can only be one of those in the same folder. You could rename "your" gtest by changing the target name in googletest/CMakelists.txt, but I would strongly advise you to not do that.

    In my opinion, gtest shouldn't even be a shared library at all, especially if you are using different build flags for different projects in your repository. There is an alternative, and that is basically only including the gtest source code in a folder, and then including the header files and source files in your unittests main.cpp. googletest already comes with helpers for that, that is src/gtest-main.cc.

    This is how I would structure it:

    1. Add the gtest version you want as submodule to git (in case you use git). This way, you have a specified version for all projects in your repo, and can update it in a different branch. I will call that folder "GTEST_DIR".
    2. Write your unittests in .cpp files, that #include <gtest/gtest.h>, one per hpp you want to test, and #include both the hpp and the cpp in your test.cpp. This enforces the separation of your tests from other classes and makes it very easy to switch out dependent classes with mocks or fake objects. You will not need a main() function, as that one is already in gtest-main.cc.

    3. Write a cmake macro like this:

      macro(add_gtest NAME FILES)
add_executable(my_gtest_$NAME
  $FILES
  GTEST_DIR/src/gtest.cc
  GTEST_DIR/src/gtest-death-test.cc
  GTEST_DIR/src/gtest-filepath.cc
  GTEST_DIR/src/gtest-port.cc
  GTEST_DIR/src/gtest-printers.cc
  GTEST_DIR/src/gtest-test-part.cc
  GTEST_DIR/src/gtest-typed-test.cc
  GTEST_DIR/src/gtest-main.cc
)
target_include_directories(my_gtest_$NAME GTEST_DIR/include)
endmacro()

    Of course, you can make this more complicated or less complicated, but that is the gist. Of course, compile times will be longer this way over using gtest as a shared library, but it actually makes sure your units get tested in isolation, which is very valueable in my opinion. Also, you can use ccache to greatly improve compile times in this scenario, because the gtest object files never change. Also, this will make sure gtest is compiled with exactly the flags you want it to. You could for example create 2 separate unit tests for the same class, one with exceptions enabled and one without.