index.php

<?php
/*
Plugin Name: Show Warning Message on Dashboard
Plugin URI: http://www.rescuework.jp/
Description: Displays warning messages on your WP's dashboard.
Author: Fumito MIZUNO
Version: 1.0
License: GPL 2.0 or later http://www.gnu.org/licenses/gpl.html
*/

/**
 * OunziwShowMessage 
 * 
 */
class OunziwShowMessage {
    protected $htmlformat = '<div class="%s"><p>%s</p></div>';
    protected $output = '';
    
    /**
     * __construct 
     * 
     * @access protected
     * @return void
     */
    function __construct() {
        add_action( 'all_admin_notices', array( $this, 'echoOutput' ) );
    }
    /**
     * setOutput 
     * 
     * @param mixed $message 
     * @param string $divclass 
     * @access public
     * @return void
     */
    function setOutput($message,$divclass='error') {
        $divclass = sanitize_html_class($divclass,'error');
        $message = wp_kses_post($message);
        $this->output .= sprintf($this->htmlformat,$divclass,$message);
    }
    /**
     * echoOutput 
     * 
     * @access public
     * @return void
     */
    function echoOutput() {
        echo $this->output;
    }
}


/**
 * OunziwCreateMessage 
 * 
 */
class OunziwCreateMessage {
    protected $obj;
    protected $message;
    /**
     * __construct 
     * 
     * @param OunziwShowMessage $obj 
     * @access protected
     * @return void
     */
    function __construct(OunziwShowMessage $obj) {
        $this->obj = $obj;
        $this->addMessage();
    }
    /**
     * addMessage 
     * 
     * @final
     * @access protected
     * @return void
     */
    final protected function addMessage(){
        if ($this->check()) {
            $this->setMessage();
            $this->obj->setOutput($this->message);
        }
    }
    /**
     * check 
     * 
     * @access protected
     * @return void
     */
    protected function check(){
        return file_exists(ABSPATH . 'wp-admin/install.php');
    }
    /**
     * setMessage 
     * 
     * @access protected
     * @return void
     */
    protected function setMessage(){
        $this->message = __('wp-admin/install.php exists! Delete this file.');
    }
}

$obj = new OunziwShowMessage;
new OunziwCreateMessage($obj);

mesageTest.php

<?php 
/*
Plugin Name: Show Warning Message on Dashboard
Plugin URI: http://www.rescuework.jp/
Description: Displays warning messages on your WP's dashboard.
Author: Fumito MIZUNO
Version: 1.0
License: GPL 2.0 or later http://www.gnu.org/licenses/gpl.html
*/

class childShowMessage extends OunziwShowMessage{
    function returnOutput() {
        ob_start();
        parent::echoOutput();
        $output = ob_get_clean();
        return $output;
    }
}
class MessageTest extends PHPUnit_Framework_TestCase {

    protected $obj;
    function setUp() {
        $this->obj = new childShowMessage;
    }

    function testOutput() {
        
        $message = 'Message';
        $expected = '<div class="error"><p>Message</p></div>';
        $this->obj->setOutput($message);
        $output = $this->obj->returnOutput();
        
        $this->assertEquals($expected, $output);
    }

    function testDefaultClass() {
        
        $message = 'Message';
        $divclass = '';
        $expected = '<div class="error"><p>Message</p></div>';
        $this->obj->setOutput($message,$divclass);
        $output = $this->obj->returnOutput();
        
        $this->assertEquals($expected, $output);
    }

    function testEscapeClass() {
        
        $message = 'Message';
        $divclass = '<script>error</script>';
        $expected = '<div class="scripterrorscript"><p>Message</p></div>';
        $this->obj->setOutput($message,$divclass);
        $output = $this->obj->returnOutput();
        
        $this->assertEquals($expected, $output);
    }

    function testEscapeMessage() {
        
        $message = '<script>Message</script>';
        $expected = '<div class="error"><p>Message</p></div>';
        $this->obj->setOutput($message);
        $output = $this->obj->returnOutput();
        
        $this->assertEquals($expected, $output);
    }

}