After creating your app, you can test your live app to see how it works.

To do this, log into your dashboard, and navigate to the left sidebar, you can click on "Apps" in the search bar.

When the apps page loads up, you can navigate to the app you'd like to test.
Click on the selected app to open it.

Then, navigate to the bottom left after it opens, you can choose to try Payments or Financial Data as shown below.

When you click on either of them, it launches your widget. You can then test either connecting an account or making a payment.

That's all you need to know for testing your app on your dashboard.