IMO having a test environment is a bit of a failure: you should be able to spin up and stop a full test environment easily, ideally (and feasibly for most systems) on the developer's local machine.
Depends on the type of testing. If you're doing integration testing between systems, then it's not just a matter of spinning it up on a developer's local machine.
You need a testing environment, especially if there are other physical elements that are being integrated (embedded and other equipment).
It's bizarre to me that we live in a world where whole machines and their networking stack can be spun up and virtualized and yet integration testing STILL actually has to go out and touch a real resource running on a different machine.
Yeah, obviously this isn't gonna work for embedded development, but not that many people have that specific problem. Is it really so hard to spin up ephemeral testing clusters on a single machine? Everywhere that I've seen it done, it's a horrible kludge of scripts and hacks that's almost as difficult to understand as the code under test.
Docker has made this much much easier than it used to be, and the ease of publishing images has led to many SaaS companies providing "dockerized" versions of their services.
I write a lot of Terraform to manage internal infrastructure with dependencies on other internal and external infrastructure that's outside of my control. I define a module parameter for each dependency (usually with a default value that points to the real service URL) and then create a second module that uses Docker to spin up and configure local instances of each dependency and overrides the corresponding parameter.
This makes local testing very straightforward: `terraform -chdir=tests apply`
Sure, for integration with some specific hardware, there may be some limits (though I would ask if that could be simulated for most testing, or if multiple could be made available). But it's a goal that should be aimed for and is achievable for most software, if some effort is spent on it. I see a lot of places seem to cargo-cult a dev/staging/prod setup (each of which inevitably winds up slightly different and hard to reproduce for incidental reasons) and it seems like an approach with a lot of headaches that you probably don't want to use unless you're forced to.
When you have a lot of interdepended systems it is not always possible. In our case our test environment cannot be replicated locally on developer machines because it integrates to various 3rd parties to which we only have one set of test credentials.
You need a testing environment, especially if there are other physical elements that are being integrated (embedded and other equipment).