With M2E Pro you can test Magento 2 and you don’t need to stop the synchronization process on your Magento v.1.
How to do the test migration?
1) The first and major thing you need to do is to import your database tables dump from Magento v1.x to the Magento v2.x
2) The imported data will be adapted to the Magento v2.x environment. After tables are transferred, you will see Step 2 of the Migration Wizard.
3) Set Disable M1 Synchronization option to No to keep synchronization on Magento v1.x running. Click Continue.
4) On Step 3, set Enable M2 Synchronization option to No. Click Complete.
That’s it! Now you can explore Magento 2 functionality and check how your data was transferred.