Testing option 1. Checking the expression
When you compose an expression using object fields, you can check it on the go, providing an object ID to deal with.
Remember, that this "Checking the expression" shows the result expression in the text area, not the step result!
Testing option 2. Checking the step
If you want to check the particular step, but not the whole scenario, you can use step testing
Moreover, if you use Context variables, you can specify their values while testing:
Testing option 3. Throwing an object into scenario
You can test the whole scenario by throwing an object in it.
Discover the test results in object or in logs.
Remember, that you can use scenario testing both for Running mode and Editing mode. Sometimes such a mechanism is useful not for testing, but for manual scenario execution.