Disable testing when using BUILD_TESTING (#1682)

Author: pfultz2

CMakeLists.txt

@@ -272,6 +272,13 @@ if(PYBIND11_INSTALL)
   endif()
 endif()
 
-if(PYBIND11_TEST OR (BUILD_TESTING AND PYBIND11_MASTER_PROJECT))
-  add_subdirectory(tests)
+# BUILD_TESTING takes priority, but only if this is the master project
+if(PYBIND11_MASTER_PROJECT AND DEFINED BUILD_TESTING)
+  if(BUILD_TESTING)
+    add_subdirectory(tests)
+  endif()
+else()
+  if(PYBIND11_TEST)
+    add_subdirectory(tests)
+  endif()
 endif()