The workflow designer lets you test a workflow before you publish it to check for any errors.

To do this, proceed as following:

1. Go to Settings > Cost management > Workflow designer.
2. Click on a workflow and enter the canvas mode.
3. 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.