When it doesn't break, it should conditionally omit the trailing space

It should omit the trailing space if it is stripped anyway
{% if a %}space {%- endif %}

It should not omit the trailing space if there's trailing whitespace
{% if a %}space {% endif %}
{%- if a %}space {% endif -%}
{% if a %}space {% endif %}

It should not omit the whitespace because of whitespace stripping outside the tag
<p>
{% if a %}aaaaaaaaaaaaaaaaaamaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa {% endif %}{{ value }}
</p>

It should not omit the whitespace if it is included inline in a paragraph
<p>haha{% if a %}space {% endif %}haha</p>