BUG: Teach VariableWatch test to check results

Previously this test was only a smoke test for manual verification.
This teaches the test to actually check that the variable watch
succeeds.

Tests/CMakeTests/VariableWatchTest.cmake.in

@@ -6,6 +6,7 @@ VARIABLE_WATCH(TESTVAR1)
 macro(testwatch var access file stack)
   MESSAGE("There was a ${access} access done on the variable: ${var} in file ${file}")
   MESSAGE("List file stack is: ${stack}")
+  set(${var}_watched 1)
 endmacro(testwatch)
 
 VARIABLE_WATCH(somevar testwatch)
@@ -17,6 +18,14 @@ set(TESTVAR "0")
 
 
 message("Variable: ${somevar}")
+if(NOT somevar_watched)
+  message(SEND_ERROR "'somevar' watch failed!")
+endif()
+set(somevar_watched)
+
 set(somevar "1")
 message("Variable: ${somevar}")
+if(NOT somevar_watched)
+  message(SEND_ERROR "'somevar' watch failed!")
+endif()
 remove(somevar)