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

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

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

When not leadingSpaceSensitive, the leading whitespace can be omitted.
<div>
  {% if a %} space{% endif %}
</div>

When leadingSpaceSensitive, the leading space can be omitted if it exists outside the tag
<span> {% if a %} space{% endif %}</span>

When leadingSpaceSensitive, the leading space cannot be omitted if it is absent outside the tag
<span>{% if a %} space{% endif %}</span>

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

It should not omit the whitespace when leadingSpaceSensitive
<p>haha{% if a %} space{% endif %}</p>

It should strip leading outer whitespace when it breaks and keep the inner leading whitespace when leadingSpaceSensitive
<p>haha{% if a %} looooooooooooooooooooooooooooooooooooooooooooooooooooooo{% endif %}</p>