Prophecy framework and drupal 7

Question

I'm trying to create a test using Phpunit and mocking with Prophecy but I'm getting MethodNotFoundException. This is my code:

<?php

namespace Drupal\forum_innovation\Tests;

use Prophecy;

/**
 * Test the  ForumCounter Class.
 * @coversDefaultClass  \Drupal\forum_innovation\Forum
 * @group utility
 */
class ForumCounterTest extends \PHPUnit_Framework_TestCase {

    /**
     * @covers::setForumCounter
     */

    public function testSetForumCounter() {

        $prophet = new Prophecy\Prophet;
        $set_counter = $prophet->prophesize('Drupal\forum_innovation\Forum\ForumCounter');

        $set_counter->setForumCounter(83, 3024)->willReturn(TRUE);

        $stub = $set_counter->reveal();

    }

}

I'm executing the test from the command line and I'm getting this error:

This is the class and methods I want to test:

<?php
namespace Drupal\forum_innovation\Forum;


class ForumCounter implements ForumInterface {


    public static function setForumCounter($forum, $uid) {
        $counterState = db_update('forum_counter_states')
            ->fields(array(
                'state' => 'read',
            ))
            ->condition('uid', $uid)
            ->condition('tid', $forum)
            ->execute();

        return $counterState;

    }

}

I don't know what is wrong with test, so, any help will be appreciate it. Thanks.