a.js

var async = require('async');

var data;

MakeUsesrHttpCall(function(err,res){
  data.users = res;
});
 
MakeTestHttpCall(function(err,res){
  data.tests = res;
});

exports.init = function(callback) {
  // you could eager return if the data is present,
  // or perhaps via a supplied optional first argument
  if (data) {
    callback(null, data);
    return;
  }
  
  data = {};
  
  async.parallel([ MakeUsesrHttpCall, MakeTestsHttpCall ], function(err) {
    callback(err, data);
  });
});
 

b.js

var a = requre('a.js');
 
a.init(function(err, data) {
  // do something with data here
})