Create a testing example

[nikku]

Is your feature request related to a problem? Please describe.

It is a valid user question if/how bpmn-js and custom integrations can be tested.

Describe the solution you'd like

• An example outlines good practices around testing bpmn-js and extensions.

Describe alternatives you've considered

Document in a blog (not preferred).

Additional context

Raised in the context of this forum post.

[nikku]

Moving to ready as a post release activity.