Provide some "step" API

[lefou]

The idea is the following: You have some longer buisiness logic, e.g. a workflow, and you want to make sure, that each step of that workflow passes some tests. In case of a failure, you want to exactly now, which step failed. Also, you want to see the steps in the test passed output.

The API should feel like this:

test("Some complex workflow", () -> {
  step("init the system", () -> {
    // do some work and some asserts
    step("next workflow step", () -> {
      // do some more work, including further tests / asserts
      // of course you can access state and results of previous steps
      ...
    }
  }
}

The output might look something like:

Running 1 test in org.example.SimpleTest:
-- Some complex workflow
---- SUCCESS Step 1: init the system
---- SUCCESS Step 2: next workflow step
-- SUCCESS Some complex workflow