One feature I've never seen in test frameworks that I think would be good: Instead of concurrency being a boolean on/off, tests should be able to declare a lis

One feature I've never seen in test frameworks that I think would be good: Instead of concurrency being a boolean on/off, tests should be able to declare a list of shared dependencies (e.g. using arbitrary string identifiers). Then the test runner could make sure no two tests with the same dependency run at the same time, but still use as much concurrency as possible. You could extend this further by marking certain dependencies as read-only, so the read-only tests can still run in parallel with each other.