Add NanoVDB volume test scaffolding

tests/CMakeLists.txt

@@ -23,8 +23,25 @@ FetchContent_Declare(
 )
 
 set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
+set(INSTALL_GTEST OFF CACHE BOOL "" FORCE)
 FetchContent_MakeAvailable(googletest)
 
+if(TARGET gtest AND NOT TARGET GTest::gtest)
+    add_library(GTest::gtest ALIAS gtest)
+endif()
+
+if(TARGET gtest_main AND NOT TARGET GTest::gtest_main)
+    add_library(GTest::gtest_main ALIAS gtest_main)
+endif()
+
+if(TARGET gmock AND NOT TARGET GTest::gmock)
+    add_library(GTest::gmock ALIAS gmock)
+endif()
+
+if(TARGET gmock_main AND NOT TARGET GTest::gmock_main)
+    add_library(GTest::gmock_main ALIAS gmock_main)
+endif()
+
 enable_testing()
 
 # ============================================================