add googletest

[shaomeng]

This PR adds GoogleTest into the CMake system, and also tests the behavior of ptr_cache.hpp.

It introduces a new build option, BUILD_GOOGLE_TEST. When it's set to TRUE, a test app will be build in the build directory:
googletest_scripts

To run this test, one can either invoke it directly: ./googletest_scripts/ptr_cache_test, or run a single ctest command: ctest . . The latter is convenient when a lot of unit test programs are there.

@ifranda Please let me know if you have any questions!

[ifranda]

Sounds great, thanks! Is the process like this?

cd ~/VAPOR
mkdir build
cd build
cmake -DBUILD_GOOGLE_TEST=ON ..

This creates some files, but also outputs this:

ifranda@casper-login2:~/VAPOR/build> cmake -DBUILD_GOOGLE_TEST=ON ..
CMAKE_BUILD_TYPE Debug
CMake Error at /usr/share/cmake/Modules/FetchContent.cmake:690 (message):
  No content details recorded for googletest
Call Stack (most recent call first):
  /usr/share/cmake/Modules/FetchContent.cmake:1064 (__FetchContent_getSavedDetails)
  /usr/share/cmake/Modules/FetchContent.cmake:1184 (FetchContent_Populate)
  CMakeLists.txt:141 (FetchContent_MakeAvailable)


-- Configuring incomplete, errors occurred!
See also "/glade/u/home/ifranda/VAPOR/build/CMakeFiles/CMakeOutput.log".

[shaomeng]

Hey @ifranda , can you do the following and retry? I think 2) is probably the cause.

1. delete all the content of the build directory, and
2. use "module load cmake" to load a newer version of cmake

[ifranda]

module load cmake did the trick!

[ifranda]

Looks good!

[shaomeng]

Hi @ifranda , could you remove the if() and endif() lines (line 132 and 136) for me? The CMake version should be specified at the beginning of the CMakeLists.txt (Line 7, cmake_minimum_required()) function, instead of here.

(I lost my access to update this PR.)

[ifranda]

Sure! I’m not at my computer right now but I’ll update it tonight or tomorrow