Reactjs 运行karma/Ezyme测试时，只允许安装一次babel polyfill

当我用酶运行karma测试时，我得到一个错误：

only one instance of babel-polyfill is allowed at ...

是导致此错误的测试文件：

import React from 'react';
import { Provider } from 'react-redux';
import configureStore from '../../src/common/store/configureStore';
import { shallow,mount } from 'enzyme';
import ChatContainer from '../../src/common/containers/ChatContainer';


const initialState = window.__INITIAL_STATE__;
const store = configureStore(initialState);




describe('ChatContainer Component', () => {
    let Component;

    beforeEach(() => {
        Component = 
            mount(<Provider store={store}>
                <ChatContainer />
            </Provider>);
    });

    it('should render', () => {
        expect(Component).toBeTruthy();
    });


});

这是我的网页配置：

var path = require('path');
var webpack = require('webpack');

module.exports = {
  devtool: 'inline-source-map',
  entry: [
    'babel-polyfill',
    'webpack-hot-middleware/client',
    './src/client/index'
  ],
  output: {
    path: path.resolve(__dirname, './static/dist'),
    filename: 'bundle.js',
    publicPath: '/dist/'
  },
  plugins: [
    new webpack.HotModuleReplacementPlugin(),
    new webpack.NoErrorsPlugin(),
    new webpack.DefinePlugin({
      'process.env': {
        NODE_ENV: JSON.stringify(process.env.NODE_ENV || 'development')
      }
    })
  ],
  module: {
    loaders: [
      {
        test: /\.js$/,
        loader: 'babel',
        query: {
          plugins: [,
            [
              'react-transform', {
                transforms: [{
                  transform: ['react-transform-hmr']
                  imports: ['react'],
                  locals: ['module']
                }, {
                  transform: 'react-transform-catch-errors',
                  imports: ['react', 'redbox-react']
                }]
              }
            ]
          ]
        },
        include: [path.resolve(__dirname, 'src')]
      },
      {
        test: /\.css?$/,
        loaders: ['style', 'raw']
      }
    ]
  }
};

var path = require('path');
var webpack = require('webpack');

module.exports = {
  devtool: 'inline-source-map',
  entry: [
    'babel-polyfill',
    'webpack-hot-middleware/client',
    './src/client/index'
  ],
  output: {
    path: path.resolve(__dirname, './static/dist'),
    filename: 'bundle.js',
    publicPath: '/dist/'
  },
  plugins: [
    new webpack.HotModuleReplacementPlugin(),
    new webpack.NoErrorsPlugin(),
    new webpack.DefinePlugin({
      'process.env': {
        NODE_ENV: JSON.stringify(process.env.NODE_ENV || 'development')
      }
    })
  ],
  module: {
    loaders: [
      {
        test: /\.js$/,
        loader: 'babel',
        query: {
          plugins: [,
            [
              'react-transform', {
                transforms: [{
                  transform: ['react-transform-hmr']
                  imports: ['react'],
                  locals: ['module']
                }, {
                  transform: 'react-transform-catch-errors',
                  imports: ['react', 'redbox-react']
                }]
              }
            ]
          ]
        },
        include: [path.resolve(__dirname, 'src')]
      },
      {
        test: /\.css?$/,
        loaders: ['style', 'raw']
      }
    ]
  }
};