The Workflow Designer lets you test a workflow before you publish it, to check for any errors.
To do this, proceed as following:
Go to Admin > Workflow Designer.
Click on a workflow and enter the canvas mode.
In the toolbar, click the Check workflow icon.
This validates the whole workflow, flagging for any errors that need to be fixed.
💡Tip
Try to fix errors iteratively, as usually they have a knock-on effect. In other words, fix errors on top of the list and then check the workflow once more.