Using reflection in javascript to get a name of a test function on failure

How can we determine the name of variable function that was called?

I have a function that acts as a test utility function to setup my test cases. Depending on the parameters passed by the test to the test utility function, certain sub-functions may or may not be executed. Sometimes these sub-functions fail and I need to know which one failed, but am not sure how to do this. In other languages, reflexion is what I would use here. Is that an option?

Here's an abstracted example of what we're doing:

exports.test_util_func = function(params, callback){
 //initialize the functions
 var a = function(callback){
  ...
  //response might be "{status:400, body: {error: {...} } }"
  callback(error, response);
 }
 var b = function(callback){
  ...
  callback(error, response);
 }
 //determine what functions to run
 var functions_to_run = [];
 if(params.a) functions_to_run.push(a);
 if(params.b) functions_to_run.push(a);
 async.series(functions, function(error, responses){
  if(error) throw new Error(error);
  for(var i in responses){(function(response){
    //verify that we received a 200 success status from the server
    //if we didn't, capture the error
    if(response.status!==200){
      console.log(response.body);
      console.log(i);
      //HELP NEEDED HERE - how do we capture better than the function iteration so we know what actually failed? Ideally, we would have: "reflective call()
      throw new Error(i+": "+JSON.stringify(response.body));
    }
  })(responses[i]);}
 })
}

Edit: there might be something in this following post that we can use, but I imagine there must be some easier way by using the __prototype info: Get variable name. javascript "reflection"