As a Flow designer, you normally build your Flow logic a few steps at a time and then would quickly test the logic built so far.
Once you are finished with logic, you publish your Flow and it becomes live to be used in your organization.

However, we all know changes are inevitable. They do happen and you would need to change your workflow logic accordingly. It can be adding or removing an approval step, creating a new branch in your logic, using e-signature instead of email approval.
So, you go ahead and make the changes but would really want to test them properly before publishing them and making the live.
Imagine you have automated your supplier invoice approval and routing process and it’s live in production. But you need to update your logic and get the department’s head approval if the invoice amount is more than $10K. In this case you first want to test your updated logic and once you are confident that the new changes work fine, only then publish your Flow to production.
The good news is that we have recently added a new feature which makes testing of your Flow a lot easier and enjoyable. The best part is that you can test your draft Flows without needing to publish them. We call the feature, Test Run.
Test Run is available from within the designer and shows you the live progress of your logic.
To use the Test Run you just need to save your changes (no need to publish them). Once you save your changes the Test Run button gets enabled.