ONNX will build googletest from a Git checkout.  Patch CMake to use our
googletest package and enable tests by default.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0aa9fda2..a573170c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,7 +22,7 @@ option(BUILD_ONNX_PYTHON "Build Python binaries" OFF)
 option(ONNX_GEN_PB_TYPE_STUBS "Generate protobuf python type stubs" ON)
 option(ONNX_WERROR "Build with Werror" OFF)
 option(ONNX_COVERAGE "Build with coverage instrumentation" OFF)
-option(ONNX_BUILD_TESTS "Build ONNX C++ APIs Tests" OFF)
+option(ONNX_BUILD_TESTS "Build ONNX C++ APIs Tests" ON)
 option(ONNX_USE_LITE_PROTO "Use lite protobuf instead of full." OFF)
 option(ONNXIFI_ENABLE_EXT "Enable onnxifi extensions." OFF)
 if(NOT DEFINED ONNX_ML)
@@ -82,8 +82,10 @@ if(CMAKE_SYSTEM_NAME STREQUAL "AIX")
 endif()

 if(ONNX_BUILD_TESTS)
-  list(APPEND CMAKE_MODULE_PATH ${ONNX_ROOT}/cmake/external)
-  include(googletest)
+  find_package(GTest REQUIRED)
+  if(NOT GTest_FOUND)
+    message(FATAL_ERROR "cannot find googletest")
+  endif()
 endif()

 if((ONNX_USE_LITE_PROTO AND TARGET protobuf::libprotobuf-lite) OR ((NOT ONNX_USE_LITE_PROTO) AND TARGET protobuf::libprotobuf))
diff --git a/cmake/unittest.cmake b/cmake/unittest.cmake
index e29a93ff..ae146390 100644
--- a/cmake/unittest.cmake
+++ b/cmake/unittest.cmake
@@ -7,7 +7,7 @@
 
 find_package(Threads)
 
-set(${UT_NAME}_libs ${googletest_STATIC_LIBRARIES})
+set(${UT_NAME}_libs ${GTEST_LIBRARIES})
 
 list(APPEND ${UT_NAME}_libs onnx)
 list(APPEND ${UT_NAME}_libs onnx_proto)
@@ -22,9 +22,9 @@
   list(REMOVE_DUPLICATES _UT_SOURCES)
 
   add_executable(${_UT_TARGET} ${_UT_SOURCES})
-  add_dependencies(${_UT_TARGET} onnx onnx_proto googletest)
+  add_dependencies(${_UT_TARGET} onnx onnx_proto)
 
   target_include_directories(${_UT_TARGET}
-                             PUBLIC ${googletest_INCLUDE_DIRS}
+                             PUBLIC ${GTEST_INCLUDE_DIRS}
                                     ${ONNX_INCLUDE_DIRS}
                                     ${PROTOBUF_INCLUDE_DIRS}
                                     ${ONNX_ROOT}