Nested Contexts to allow easier hierarchical tests

[pesse]

To make it easier to structure the tests (as described in this video by Kevlin Henney: https://www.youtube.com/watch?v=tWn8RA_DEic) it would be great to allow nesting of contexts:

create or replace package queue_spec as
  -- %suite(Queue Spec)
  
  -- %context(a_not_empty_queue)
    
    -- %context(that_is_not_full)
      -- %test
      procedure becomes_longer_when_non_null_value_enqueued;
      -- %test
      procedure becomes_full_when_enqueued_up_to_capacity;
    -- %endcontext
    
    -- %context(that_is_full)
      -- %test
      procedure ignores_further_enqueued_values;
      -- %test
      procedure becomes_non_full_when_dequeued;
    -- %endcontext

    -- %test
    procedure dequeues_values_in_order_enqueued;

  -- %endcontext
end;

Leading to

Queue Spec
  a_not_empty_queue
    that_is_not_full
      becomes_longer_when_non_null_value_enqueued [SUCCESS]
      becomes_full_when_enqueued_up_to_capacity [SUCCESS]
    that_is_full
      ignores_further_enqueued_values [SUCCESS]
      becomes_non_full_when_dequeued [SUCCESS]
    dequeues_values_in_order_enqueued [SUCCESS]

What to do in case of missing endcontext?
Write a warning