Add support for GTest based unit tests. (#485)

* Add support for GTest based unit tests.

As Dominic and I have previously discussed, there is some
need/desire to improve the testing situation in Google Benchmark.

One step to fixing this problem is to make it easier to write
unit tests by adding support for GTest, which is what this patch does.

By default it looks for an installed version of GTest. However the
user can specify -DBENCHMARK_BUILD_EXTERNAL_GTEST=ON to instead
download, build, and use copy of gtest from source. This is
quite useful when Benchmark is being built in non-standard configurations,
such as against libc++ or in 32 bit mode.

1 files changed, 77 insertions, 0 deletions

diff --git a/cmake/HandleGTest.cmake b/cmake/HandleGTest.cmake
new file mode 100644
index 0000000..c84f653
--- /dev/null
+++ b/cmake/HandleGTest.cmake
@@ -0,0 +1,77 @@
+
+macro(split_list listname)
+  string(REPLACE ";" " " ${listname} "${${listname}}")
+endmacro()
+
+macro(build_external_gtest)
+  include(ExternalProject)
+  set(GTEST_FLAGS "")
+  if (BENCHMARK_USE_LIBCXX)
+    if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+      list(APPEND GTEST_FLAGS -stdlib=libc++)
+    else()
+      message(WARNING "Unsupported compiler (${CMAKE_CXX_COMPILER}) when using libc++")
+    endif()
+  endif()
+  if (BENCHMARK_BUILD_32_BITS)
+    list(APPEND GTEST_FLAGS -m32)
+  endif()
+  if (NOT "${CMAKE_CXX_FLAGS}" STREQUAL "")
+    list(APPEND GTEST_FLAGS ${CMAKE_CXX_FLAGS})
+  endif()
+  string(TOUPPER "${CMAKE_BUILD_TYPE}" GTEST_BUILD_TYPE)
+  if ("${GTEST_BUILD_TYPE}" STREQUAL "COVERAGE")
+    set(GTEST_BUILD_TYPE "DEBUG")
+  endif()
+  split_list(GTEST_FLAGS)
+  ExternalProject_Add(googletest
+      EXCLUDE_FROM_ALL ON
+      GIT_REPOSITORY https://github.com/google/googletest.git
+      GIT_TAG master
+      PREFIX "${CMAKE_BINARY_DIR}/googletest"
+      INSTALL_DIR "${CMAKE_BINARY_DIR}/googletest"
+      CMAKE_CACHE_ARGS
+        -DCMAKE_BUILD_TYPE:STRING=${GTEST_BUILD_TYPE}
+        -DCMAKE_C_COMPILER:STRING=${CMAKE_C_COMPILER}
+        -DCMAKE_CXX_COMPILER:STRING=${CMAKE_CXX_COMPILER}
+        -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR>
+        -DCMAKE_CXX_FLAGS:STRING=${GTEST_FLAGS}
+        -Dgtest_force_shared_crt:BOOL=ON
+      )
+
+  ExternalProject_Get_Property(googletest install_dir)
+
+  add_library(gtest UNKNOWN IMPORTED)
+  add_library(gtest_main UNKNOWN IMPORTED)
+
+  set(LIB_SUFFIX "${CMAKE_STATIC_LIBRARY_SUFFIX}")
+  set(LIB_PREFIX "${CMAKE_STATIC_LIBRARY_PREFIX}")
+
+  if("${GTEST_BUILD_TYPE}" STREQUAL "DEBUG")
+    set(LIB_SUFFIX "d${CMAKE_STATIC_LIBRARY_SUFFIX}")
+  endif()
+  file(MAKE_DIRECTORY ${install_dir}/include)
+  set_target_properties(gtest PROPERTIES
+    IMPORTED_LOCATION ${install_dir}/lib/${LIB_PREFIX}gtest${LIB_SUFFIX}
+    INTERFACE_INCLUDE_DIRECTORIES ${install_dir}/include
+  )
+  set_target_properties(gtest_main PROPERTIES
+    IMPORTED_LOCATION ${install_dir}/lib/${LIB_PREFIX}gtest_main${LIB_SUFFIX}
+    INTERFACE_INCLUDE_DIRECTORIES ${install_dir}/include
+  )
+  add_dependencies(gtest googletest)
+  add_dependencies(gtest_main googletest)
+  set(GTEST_BOTH_LIBRARIES gtest gtest_main)
+  #set(GTEST_INCLUDE_DIRS ${install_dir}/include)
+endmacro(build_external_gtest)
+
+if (BENCHMARK_ENABLE_GTEST_TESTS)
+  if (IS_DIRECTORY ${CMAKE_SOURCE_DIR}/googletest)
+    add_subdirectory(${CMAKE_SOURCE_DIR}/googletest)
+    set(GTEST_BOTH_LIBRARIES gtest gtest_main)
+  elseif(BENCHMARK_DOWNLOAD_DEPENDENCIES)
+    build_external_gtest()
+  else()
+    find_package(GTest REQUIRED)
+  endif()
+endif()