Node.jsで単体testを書く際に，モジュールをstubに置き換える ref: https://qiita.com/wicket/items/af9a5d74608bedf97a85

file0.txt

var moduleStubs = {};
var originalJsLoader = require.extensions['.js'];

var stubOnModule = function(module) {
  var path          = require.resolve(module);
  var stub           = sinon.stub();
  moduleStubs[path] = stub;
  delete require.cache[path];
  return stub;
};

require.extensions['.js'] = function (obj, path) {
  if (moduleStubs[path])
    obj.exports = moduleStubs[path];
  else
    return originalJsLoader(obj, path);
};

afterEach(function() {
  for (var path in moduleStubs) {
    delete moduleStubs[path];
  }
});

file1.txt

it('test', function(){
  stubOnModule("module");

  var m = require("module"); //return stub

  var instance = new m(); // OK
  var value = m.b; // ok

  m.a(); // error : m.a is not a function
  var value = m.c.d; // error : Cannot read property 'd' of undefined
  var instance2 = new m.A({}); // error : ws.Server is not a constructor

});

file2.txt

it('test', function(){
  var stub = stubOnModule("module");
  stub.a = sinon.stub();
  stub.c = sinon.stub();
  stub.c.d = sinon.stub();
  stub.A = sinon.stub();

  var m = require("module"); //return stub


  m.a(); // error : m.a is not a function
  var value = m.c.d; // error : Cannot read property 'd' of undefined
  var instance2 = new m.A({}); // error : m.A is not a constructor

});