test(z): ensure ngltools Qt smoke test is added when BUILD_TESTING is ON (avoid TARGET guard)

Z/src/ngltools/CMakeLists.txt

@@ -25,7 +25,7 @@ NGL_TARGET_LINK_LIBRARIES(ngltools
 )
 
 # Smoke test for ngltools DTG conversion utilities
-IF(BUILD_TESTING AND TARGET ngltools)
+IF(BUILD_TESTING)
   find_package(Qt6 COMPONENTS Test Core QUIET)
   if (Qt6_FOUND)
     set(_QTTEST_TARGET Qt6::Test)
@@ -36,9 +36,11 @@ IF(BUILD_TESTING AND TARGET ngltools)
     set(_QTCORE_TARGET Qt5::Core)
   endif()
 
-  add_executable(ngltools_qt_smoke tests/NGLToolsQtSmokeTest.cpp)
-  target_link_libraries(ngltools_qt_smoke PRIVATE ngltools ${_QTTEST_TARGET} ${_QTCORE_TARGET})
-  add_test(NAME NGLToolsQtSmoke COMMAND ngltools_qt_smoke)
+  if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/tests/NGLToolsQtSmokeTest.cpp)
+    add_executable(ngltools_qt_smoke tests/NGLToolsQtSmokeTest.cpp)
+    target_link_libraries(ngltools_qt_smoke PRIVATE ngltools ${_QTTEST_TARGET} ${_QTCORE_TARGET})
+    add_test(NAME NGLToolsQtSmoke COMMAND ngltools_qt_smoke)
+  endif()
 ENDIF()
 NGL_TARGET_COMPILE_DEFINITIONS(ngltools PUBLIC BUILD_BASE_PATH="${CMAKE_BINARY_DIR}")
 NGL_TARGET_COMPILE_DEFINITIONS(ngltools PUBLIC INSTALL_PREFIX="${CMAKE_INSTALL_PREFIX}")