WP_Query parameter conflict

Is your post type non-hierarchical like a post – or hierarchical like a page?
It will determine which slug parameter you should be using in WP_Query:

name (string) - non-hierarchical (post) slug.
pagename (string) - hierarchical (page) slug.

Also, the tax_query should have the operator parameter. Possible values are ‘IN’, ‘NOT IN’, ‘AND’. You should set it to ‘AND’.
This could be a solution:

$args = array(
    'post_type'=>'specialist',
    'postname' => 'test',
    'tax_query' => array(
        array(
            'taxonomy' => 'type',
            'field' => 'slug',
            'terms' => 'therapist',
            'operator'=> 'AND'
        )
    )
);

$specialists = new WP_Query($args);

If it really isn’t working, then you could always do a workaround by creating a filtering function to add the where clause to the query

function filter_where( $where="" ) {
    // post_name
    $where .= " AND $wpdb->posts.post_name="test"";
    return $where;
}
add_filter( 'posts_where', 'filter_where' );
$query = new WP_Query( $args );
remove_filter( 'posts_where', 'filter_where' );

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