public static String accessMultiDexMethod(){


        String ret = "enable multiDexEnabled & uncomment accessMultiDexMethod";
        /**
         * test for extra dex
         * this case for : test whether class of extra dex can be accessed, after extra dex is loaded.
         */
        {
            /*retrofit2.Retrofit retrofit = new retrofit2.Retrofit.Builder()
                    .baseUrl("http://www.mocky.io/v2/")
                    .addConverterFactory(retrofit2.converter.gson.GsonConverterFactory.create())
                    .build();
            Log.d(TAG, "retrofit:" + retrofit.baseUrl());
            ret = "retrofit baseUrl: " + retrofit.baseUrl();*/
        }

        /**
         * test for main dex
         * this case for : test whether class of main dex can be still accessed, after extra dex is loaded.
         */
        {
            /*int autoHeight = com.google.android.gms.ads.AdSize.AUTO_HEIGHT;
            ret += "\nAdSize.AUTO_HEIGHT: " + autoHeight;*/
        }

        /**
         * test for extra dex
         * this case for : test whether class of extra dex can be still accessed again, after extra dex is loaded
         *                 and accessing class of main dex.
         */
        {
            /*retrofit2.Retrofit retrofit = new retrofit2.Retrofit.Builder()
                    .baseUrl("http://www.mocky.io/v2/")
                    .addConverterFactory(retrofit2.converter.gson.GsonConverterFactory.create())
                    .build();
            Log.d(TAG, "retrofit:" + retrofit.baseUrl());
            ret += "\nretrofit baseUrl again: " + retrofit.baseUrl();*/
        }

        return ret;
    }
test code for multidex
test access method of retrofit, cos it will be build to extra dex normally.
you can test other methods in extra dex, According to the actual situation
replugin-sample/plugin/plugin-demo2/app/src/main/java/com/qihoo360/replugin/sample/demo2/testcase/TestMultiDex.java