Ask HN: How many test environments do you have?

At work, on a new project, we are discussing how many different environments we should have for a system.

The current consensus is that we should have a Production environment (with +1 and -1 slots) and a Test environment (with +1 and -1 slots).

The deployment process would go like this:

1. Deployment to Test +1

2. Testing on Test +1

3. Test +1 -> Test -> Test -1

4. Testing on Test

5. Deployment to Production +1

6. Testing on Production +1

7. Production +1 -> Production -> Production -1

8. Testing on Production

The idea is that tests on Production +1 would mimic how tests should perform on production, while tests on Test and Test +1 should ensure the move from Production +1 -> Production will be smooth.

What alternatives are you taking up and what do you consider "best practice" and why?