diff -burN InsightToolkit-4.12.0.orig/Modules/ThirdParty/VNL/src/CMakeLists.txt InsightToolkit-4.12.0/Modules/ThirdParty/VNL/src/CMakeLists.txt
--- InsightToolkit-4.12.0.orig/Modules/ThirdParty/VNL/src/CMakeLists.txt	2017-08-22 11:53:55.960938649 +0200
+++ InsightToolkit-4.12.0/Modules/ThirdParty/VNL/src/CMakeLists.txt	2017-08-22 11:56:07.289820954 +0200
@@ -18,10 +18,14 @@
 # Retrive the variable type to CACHE.
 set(BUILD_EXAMPLES ${BUILD_EXAMPLES} CACHE BOOL "Build the examples from the ITK Software Guide." FORCE)
 
-foreach(lib itkvcl itkv3p_netlib itktestlib itkvnl itkvnl_algo itknetlib)
+foreach(lib itkvcl itkv3p_netlib itkvnl itkvnl_algo itknetlib)
   itk_module_target(${lib} NO_INSTALL)
 endforeach()
 
+if(BUILD_TESTING)
+  itk_module_target(itktestlib NO_INSTALL)
+endif()
+
 foreach(exe
     netlib_integral_test
     netlib_lbfgs_example
diff -burN InsightToolkit-4.12.0.orig/Modules/ThirdParty/VNL/src/vxl/core/CMakeLists.txt InsightToolkit-4.12.0/Modules/ThirdParty/VNL/src/vxl/core/CMakeLists.txt
--- InsightToolkit-4.12.0.orig/Modules/ThirdParty/VNL/src/vxl/core/CMakeLists.txt	2017-08-22 11:53:55.960938649 +0200
+++ InsightToolkit-4.12.0/Modules/ThirdParty/VNL/src/vxl/core/CMakeLists.txt	2017-08-22 11:56:56.410150930 +0200
@@ -131,8 +131,10 @@
   set(CORE_VIDEO_FOUND OFF CACHE INTERNAL "VXL core video libraries built")
 endif ()
 
-# common test executable
-add_subdirectory(testlib)
+# common test executable if testing enabled
+if(BUILD_TESTING)
+  add_subdirectory(testlib)
+endif()
 
 # Tests that check and output the vxl configuration
 # NOTE: some external projects remove the tests directory (aka ITK)
