Integration tests for element templates

[jarekdanielak]

What should we do?

We should be able to integration test element templates in Desktop Modeler.

Why should we do it?

This is a follow up to a comment in integrating Element Templates Runtime Versions feature of bpmn-js-element-templates.

With new features in element templates module, we should be able to tell that:

• changes don't break the existing element templates features,
• new features work as expected.

How we do it is to be determined.