See the documentation here: https://docs.mendix.com/refguide/debug-microflows-and-nanoflows/
When running your model locally you can set breakpoints on your microflow and step through it to see what is happening. And you could even debug a live environment this way when you connect the debugger to a licensed node.
In addition to Ronald’s answer, there is also the Unit Testing module.
This allows you to test microflows automatically and is really useful when working on a project to test changes you’ve made doesn’t break any other functionality. It works best if your break your microflows down into smaller, testable sub microflows.
I hope this helps.