Creating Add-Ins for Expression Web 4
Fortunately there is a tool called the “Add-in Builder” to help with that part. IT is available via the Expression Web blog. To further add in constructing add-ins, Erik Mikkelson has created a test harness that shows the outputs, errors, and events that arise from the extensions. He is referring to this tool as the Extensibility Tester.
InfoQ Sep 01, 2015