Testing ECP-based applications often take quite some effort for setup and preparation.
I have created a Docker-based workbench that allows you to have it quick at hands.
And if you crash it? You just give your containers a fresh start.
The whole setup runs code-based during the start-up of your instance.
In that sense, it is also a portable coding example using ZPM and the objectscript-docker-template

 see Video

Working with community images from intersystemsdc is quite comfortable
Though there are limits that are fine for distribution but not so fine for development.
I want to share with you my personal hacks that make it simpler.

Migration from Caché to IRIS can be quite a challenge if your code is grown over many years
and probably not so clean structured as you may like it. So you face the need to check your
migrated code against some reference data. A few samples might not be a problem,
but some hundred GB of data for testing might be.  

A possible step could be to have your fresh code in IRIS but leave your huge datastore on Caché and connect both environments over ECP.  I have created a demo project that gives you the opportunity to try this based on 2 Docker images with IRIS and with Caché connected over ECP.

Inspired by  @Evgeny Shvarov  and his recent article 
Deploying InterSystems IRIS Embedded Python Solutions with ZPM Package Manager
I propagated the idea forward to do the same also for modules in Node.js.
The case is based on my example of IRIS Native API for Node.js.

To anticipate the obvious reply that InterSystems IRIS supports WebSockets natively as a client:
This is correct and here is my aged related article with the link to the example in OEX