How can I substitute variable in JS?

I'm trying to write unit-test. I have a simple module:

var Common = module.exports = {
  unit: {
    somejQueryFn: function() { $('.selector') /* work with jQuery */ }
  }
}

Unit-test code:

describe('Test jQuery spec', function(){
  var Common = require('common');
  it('not working :( ', function(){
     //Work. I'm using jsdom, for using jQuery in tests; It's a jQuery instance
    expect( typeof $ ).toBe('function');

    //$ is undefined in somejQueryFn; 
    expect( Common.unit.somejQueryFn() ).toBe( result );
  })
})

So, how can I handle it? Any ideas? I have tried using new Function(), but i think that is not a good idea.