CXX Tests: Fix the success check of the test generation

The variable FAILED is never defined, therefore the if condition was
never met.

We now check for the existence of the generated file which and then
output the result of the command.

Author: t-b

cpp_test_suite/cxxtest/CMakeLists.txt

@@ -7,14 +7,16 @@ endif()
 
 macro(CXX_GENERATE_TEST name)
     message("Generate ${name}.cpp")
+    set(GENERATED_FILE "${CMAKE_CURRENT_SOURCE_DIR}/${name}.cpp")
     execute_process(COMMAND "${PYTHON_INTERPRETER}" cxxtestgen.py
             --template=${CMAKE_CURRENT_SOURCE_DIR}/template/tango_template.tpl
-            -o ${CMAKE_CURRENT_SOURCE_DIR}/${name}.cpp
+            -o ${GENERATED_FILE}
             ../../new_tests/${name}.cpp
-        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/bin)
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/bin
+        RESULT_VARIABLE GENERATOR_OUTPUT)
 
-    if(${FAILED})
-        message(SEND_ERROR " Failed to generate ${name}.cpp. rv=${FAILED}")
+    if(NOT EXISTS ${GENERATED_FILE})
+      message(SEND_ERROR " Failed to generate ${name}.cpp due to \"${GENERATOR_OUTPUT}\".")
     endif()
 
     add_executable(${name} $<TARGET_OBJECTS:compare_test_object> ${name}.cpp)