added a test

tests/Aggregation/Pipeline/AvgBucketAggregationTest.php

+<?php
+
+/*
+ * This file is part of the ONGR package.
+ *
+ * (c) NFQ Technologies UAB <info@nfq.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace ONGR\ElasticsearchDSL\Tests\Aggregation\Pipeline;
+
+use ONGR\ElasticsearchDSL\Aggregation\Pipeline\AvgBucketAggregation;
+
+/**
+ * Unit test for avg_bucket aggregation.
+ */
+class AvgBucketAggregationTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * Tests getArray method.
+     */
+    public function testGetArray()
+    {
+        $aggregation = new AvgBucketAggregation('foo', 'foo>bar');
+
+        $this->assertEquals(['buckets_path' => 'foo>bar'], $aggregation->getArray());
+    }
+
+    /**
+     * Tests getType method.
+     */
+    public function testAvgBucketAggregationGetType()
+    {
+        $aggregation = new AvgBucketAggregation('foo', 'foo>bar');
+        $this->assertEquals('avg_bucket', $aggregation->getType());
+    }
+}