How to migrate multi-step deployment stages in Pipelines to use environment and concurrency-group?

[Stefan Fußenegger]

Is there an easy guide to migrate existing multi-step deployment stages to the new environment and concurrency-group properties? I'm especially looking at getting automatic resume of paused builds (= deployments). In the article Evolving deployments in Bitbucket Pipelines: Concurrency Groups and Environments there is this explanation:

Today, you still do need to use the deployment keyword in order to get deployment tracking for your pipeline. In order to get the benefit of automated step queueing AND deployment tracking at the same time, simply add both a deployment and a concurrency-group property to your step.

The concurrency-group logic will take precedent over the deployment lock, providing automated queueing and resumption of steps when multiple run at the same time targeting the same concurrency-group.

But what about existing deployment stages with multiple steps? Can I simply move the steps out of the stage and steps with the same deployment and concurrency-group values will be treated the same as a stage? Meaning consecutive steps will be completed before another pipeline can access the step? Or could a second concurrent pipeline build run step 1 right after a first pipeline finished step 1 but before it can complete step 2. So assuming pipelines #1 and #2 running 2 steps each, say deploy and test, could it be that the order of execution is

1. #1 deploy
2. #2 deploy
3. #1 test
4. #2 test

or will it always be

1. #1 deploy
2. #1 test
3. #2 deploy
4. #2 test

obviously the latter is what I'd be looking for