Remove duplicated entries from SuperTable related entries
The simplest way is to create a "filtered" array, containing the unique cables, and then loop through that.

For example:

{# Build the "filtered" array of cables #}
{% set filteredCables = [] %}

{% for row in entry.tests %}
    {% for cable in row.cables %}
        {% if cable.title not in filteredCables %}
            {% set filteredCables = filteredCables|merge([cable.title]) %}
        {% endif %}
    {% endfor %}
{% endfor %}

{# Output the unique cables #}
{% for cable in filteredCables %}
    {{ cable }}&lt;br /&gt;
{% endfor %}