wp/tests/phpunit/includes/functions.php

<?php

// For adding hooks before loading WP
function tests_add_filter($tag, $function_to_add, $priority = 10, $accepted_args = 1) {
	global $wp_filter, $merged_filters;

	$idx = _test_filter_build_unique_id($tag, $function_to_add, $priority);
	$wp_filter[$tag][$priority][$idx] = array('function' => $function_to_add, 'accepted_args' => $accepted_args);
	unset( $merged_filters[ $tag ] );
	return true;
}

function _test_filter_build_unique_id($tag, $function, $priority) {
	global $wp_filter;
	static $filter_id_count = 0;

	if ( is_string($function) )
		return $function;

	if ( is_object($function) ) {
		// Closures are currently implemented as objects
		$function = array( $function, '' );
	} else {
		$function = (array) $function;
	}

	if (is_object($function[0]) ) {
		return spl_object_hash($function[0]) . $function[1];
	} else if ( is_string($function[0]) ) {
		// Static Calling
		return $function[0].$function[1];
	}
}

function _delete_all_posts() {
	global $wpdb;

	$all_posts = $wpdb->get_col("SELECT ID from {$wpdb->posts}");
	if ($all_posts) {
		foreach ($all_posts as $id)
			wp_delete_post( $id, true );
	}
}