How to make sure TestNG runs methods on test classes in succession instead of interleaved?

Question

The situation and the problem

I have several test classes, each with several test methods. All tests use the same test database in the background. Each test class

Answer 1

Use method interceptors (=write and enable a custom one) to control the ordering.

Also, each class might use its own database sandbox: wrapping each test class into a transaction might possibly help.

Having individual suffix for tables/db set up for each class would even let your test methods run in parallel (I guess the first two options would not).