unit testing with mocha not finding function

So I'm trying to unit test a function I wrote here is the function:

function compareServices(service1, service2) {
  if (service1.name != service2.name) {
    return false
  }
  if (service1.port != service2.port) {
    return false
  }
  if (service1.target != service2.target) {
    return false
  }
  if (service1.address != service2.address) {
    return false
  }

  return true
}

it is located inside my main.js file. Now When I try to run the test I get an error saying:

 Main #compareServices() should compare if two services match:
 TypeError: main.compareServices is not a function
  at Context.<anonymous> (test/stelaSpec.js:21:25

And here is my test file:

var expect = require("chai").expect;
var main = require("../src/main.js");

describe("Main", function(){
  describe('#compareServices()', function() {
    it('should compare if two services match', function() {
      var svc1 = {
        "name": "test.fg.service",
        "port": 8001,
        "target": "mac-book",
        "address": "192.2.2.2"
      }

      var svc2 = {
        "name": "test.fg.service",
        "port": 8001,
        "target": "mac-book",
        "address": "192.2.2.2"
      }

      var result = main.compareServices(svc1, svc2);

      expect(result).equal(true)
    });
  });
});

Why is it saying it is not a function when it is?