How to write a Tax Query that matches all terms in an array?

I believe changing your operator to ‘AND’ like below will work:

$selectedOptions = array('test-attribute', 'test3');

$args=array(
  'post_type' => 'product',
  'post_status' => 'publish',
  'posts_per_page' => -1,
  'tax_query'           => array(
        array(
            'taxonomy'      => 'pa_filterable-attribute',
            'terms'         => $selectedOptions,
            'field'         => 'slug',
            'operator'      => 'AND'
        )
    )
);