Code example written for http://pablovallejo.me/debugging-wp-ajax/

wp-ajax.php

<?php

/**
* Function that will handle post insertion with data from
* POST request.
*
* <code>
*
*  // Sample returned response
*	 ( object ) array( 'status'=> 200, 'post_id' => 10 );
*
* <code>
*
* Note: you should validate your data before creating a
* WordPress Post.
*/
function ajax_create_post() {

	// Set post data up.
	$data = array(
			'post_title' => $_POST[ 'post_title' ]
		,	'post_content'  => $_POST[ 'post_content' ]
	);

	// Create a response object.
	$response = ( object ) array(
			'status' => 600
	);

	// Create a post.
	$post_id = wp_insert_post( $data );

	// Check whether the post was inserted.
	if ( is_numeric( $post_id ) ) {
		$response->status = 200;
		$response->post_id = $post_id;
	}

	// Print response.
	echo json_encode( $response );
	die();


}


// Bind action "wp_ajax_ajax_create_post" to "ajax_create_post" function.
add_action( 'wp_ajax_ajax_create_post', 'ajax_create_post' );

// Set the _POST attributes you want to use.
$_POST = array(
    'post_title' => 'My post title'
  ,	'post_content' => 'Sample post inserted via AJAX'
);

// Trigger action
do_action( 'wp_ajax_ajax_create_post' );