code: func (m *MockFileSystem) Open(arg0 string) (io.ReadWriteCloser, error) {
  	ret := m.ctrl.Call(m, "Open", arg0)
  	ret0, _ := ret[0].(io.ReadWriteCloser)
  	ret1, _ := ret[1].(error)
  	return ret0, ret1
  }
docs: // Open mocks base method