private void _testReturnMode(string id, ReturnMode mode, PValue retVal)
{
var fctx = target.Functions[id].CreateFunctionContext(engine);
engine.Process(fctx);
Assert.AreEqual(fctx.ReturnMode, mode,
"Return mode for function " + id + " does not match.");
Assert.IsTrue((bool) retVal.Equality(fctx, fctx.ReturnValue).Value,
"Return value for function " + id + " does not match.");
}