Your concerns are real, but they are a separate problem.
Regardless of the downstream testing/integration concerns, I work with projects with multiple environments, ranging from current Rails apps to a Rails 2 application (that lives in a VERY isolated environment as an internal-app for a cheap "customer"), with various things in between. I also contribute to some open source projects that want weird environments.
I've got those projects on my plate regardless of your downstream concerns (which are very valid). However, Docker lets me work on each of them in isolation from one another, and also in a way where none of the goofiness is leaking out into my dev workstation.
Prior to spinning it up in Docker, the Rails 2 app I mentioned could only be worked on in production because setting up a dev environment for it that didn't require removing all the modern stuff was effectively impossible. So while I'm embarrassed to still support that project, at least I have a way to do so and a transition path forward.
Regardless of the downstream testing/integration concerns, I work with projects with multiple environments, ranging from current Rails apps to a Rails 2 application (that lives in a VERY isolated environment as an internal-app for a cheap "customer"), with various things in between. I also contribute to some open source projects that want weird environments.
I've got those projects on my plate regardless of your downstream concerns (which are very valid). However, Docker lets me work on each of them in isolation from one another, and also in a way where none of the goofiness is leaking out into my dev workstation.
Prior to spinning it up in Docker, the Rails 2 app I mentioned could only be worked on in production because setting up a dev environment for it that didn't require removing all the modern stuff was effectively impossible. So while I'm embarrassed to still support that project, at least I have a way to do so and a transition path forward.