Test if a post is in a specific taxonomy

in_tax.php

<?php
/*
** $taxonomy = Taxonomies to retrieve terms from
** $tax = Term slug or id to test against
*/
function in_tax($taxonomy, $tax){
	global $post;
	$taxes = array();
	if(is_int($tax)){
		$terms = wp_get_object_terms($post->ID, $taxonomy, array('fields' => 'ids'));
	}else{
		$terms = wp_get_object_terms($post->ID, $taxonomy);
		foreach($terms as $term){
			$taxes[] = $term->slug;
		}
	
		$terms = $taxes;
	}
	 
	return in_array($tax, $terms);
}