It is possible to randomize test participants in your study without influencing the data you will collect once the study is live.
You can add and test the randomization in your study before it goes live - it is possible to randomize your test participant(s) to check if the randomization settings you have chosen are working correctly without concern over influencing the data you will collect later.
What is important to know is that this testing has to be done before the study is set to go live.
When setting the study to live for the first time, you will be asked whether you want to reset the randomization:
Resetting the randomization here means that all randomization information for existing participants will be removed and with that, the test participants that were randomized will not influence the future randomization of the real participants.
That means that you can start including and randomizing participants with clean randomization blocks.
The option to reset randomization is only offered when the study is set to live for the very first time - if you have previously set your study to live, you will not be able to reset the randomization.
This also means that you shouldn't randomize real participants before setting the study live for the first time.
Before you reset the randomization, please make sure all the data in the study is test data. If you are unsure.