Add googletest as a git submodule. (#756)

- Add the submodule.
- Update the build to use googletest sources from the submodule.
- Update the github test build checkout action to include submodules.
- Update build instructions to include the submodule update.

.github/workflows/test.yml

@@ -24,6 +24,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2
+        with:
+          submodules: true
       - run: git clone https://github.com/google/googletest.git ../googletest
       - run: mkdir _gh_build
       - run: cmake -G "${{ matrix.generator }}" -DENABLE_TESTS=ON ..

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "third_party/googletest"]
+	path = third_party/googletest
+	url = https://github.com/google/googletest.git

BUILDING.md

@@ -114,17 +114,26 @@ $ cmake ../ -DDRACO_SANITIZE=address
 Googletest Integration
 ----------------------
 
-Draco includes testing support built using Googletest. To enable Googletest unit
-test support the DRACO_TESTS cmake variable must be turned on at cmake
-generation time:
+Draco includes testing support built using Googletest. The Googletest repository
+is included as a submodule of the Draco git repository. Run the following
+command to clone the Googletest repository:
+
+~~~~~ bash
+$ git submodule update --init
+~~~~~
+
+To enable Googletest unit test support the DRACO_TESTS cmake variable must be
+turned on at cmake generation time:
 
 ~~~~~ bash
 $ cmake ../ -DDRACO_TESTS=ON
 ~~~~~
 
-When cmake is used as shown in the above example the googletest directory must
-be a sibling of the Draco repository root directory. To run the tests execute
-`draco_tests` from your build output directory.
+To run the tests execute `draco_tests` from your build output directory:
+
+~~~~~ bash
+$ ./draco_tests
+~~~~~
 
 WebAssembly Decoder
 -------------------

cmake/draco_tests.cmake

@@ -69,14 +69,15 @@ list(
     "${draco_src_root}/point_cloud/point_cloud_test.cc")
 
 list(APPEND draco_gtest_all
-            "${draco_root}/../googletest/googletest/src/gtest-all.cc")
+            "${draco_root}/third_party/googletest/googletest/src/gtest-all.cc")
 list(APPEND draco_gtest_main
-            "${draco_root}/../googletest/googletest/src/gtest_main.cc")
+            "${draco_root}/third_party/googletest/googletest/src/gtest_main.cc")
 
 macro(draco_setup_test_targets)
   if(DRACO_TESTS)
     if(NOT (EXISTS ${draco_gtest_all} AND EXISTS ${draco_gtest_main}))
-      message(FATAL "googletest must be a sibling directory of ${draco_root}.")
+      message(FATAL_ERROR
+              "googletest missing, run git submodule update --init")
     endif()
 
     list(APPEND draco_test_defines GTEST_HAS_PTHREAD=0)

third_party/googletest

@@ -0,0 +1 @@
+Subproject commit 703bd9caab50b139428cea1aaff9974ebee5742e