Wrong parent loop context in twig - loops

Question

I'm using Symfony 2.3 and Twig 1.15. I've got a nested foreach twig loop and I'm trying to get a different result for the last iteration of the outer loop.
I've seen this: http://twig.sensiolabs.org/doc/recipes.html#accessing-the-parent-context-in-nested-loops
However I'm getting a different result - an error in the line where I access the parent context:
Key "loop" for array with keys "groups, scores, type, user, assetic, app, avatarsDir, sonata_block, _parent, _seq, group, _key, subgroup" does not exist in "(...)"
the relevant code, stripped of classes, ids and unnecessary tags:
{% for group in groups %}
<div>
{% for subgroup in group.subgroups %}
{% for test in subgroup.tests %}
{% block test_block_box %}
{% if not loop.parent.loop.last %}
(html follows...)
{% else %}
(some different html follows...)
{% endif %}
{% endblock %}
{% endfor %}
{% endfor %}
</div>
{% endfor %}
I have made sure that the error does not refer to the inner loop call, i.e. I replaced loop.parent.loop.last with loop.last and the page rendered successfully (contents obviously wrong, but it didn't crash).
What am I doing wrong when accessing the parent context??

Answer 1

Simply remove {% block test_block_box %} and {% endblock %}, the loop parent shoud be accessible.
You can try to define a value outside of the {% block %} and see if you have access to it in the {% block %}:
{% for group in groups %}
<div>
{% for subgroup in group.subgroups %}
{% for test in subgroup.tests %}
{% set test_loop_is_last = loop.last %} {# define the value #}
{% block test_block_box %}
{% if not test_loop_is_last %}{#test the value #}
(html follows...)
{% else %}
(some different html follows...)
{% endif %}
{% endblock %}
{% endfor %}
{% endfor %}
</div>
{% endfor %}