Added sub aggregations setter in AbstractAggregation

Aggregation/FilterAggregationTest.php

@@ -69,7 +69,7 @@ class FilterAggregationTest extends \PHPUnit_Framework_TestCase
             ->method('getName')
             ->willReturn('agg_test_agg2');
 
-        $aggregation->aggregations->add($aggregation2);
+        $aggregation->addAggregation($aggregation2);
 
         $result = [
             'agg_test_agg' => [

Aggregation/GlobalAggregationTest.php

@@ -41,7 +41,7 @@ class GlobalAggregationTest extends \PHPUnit_Framework_TestCase
         // Case #1 nested global aggregation.
         $aggregation = new GlobalAggregation('test_agg');
         $aggregation2 = new GlobalAggregation('test_agg_2');
-        $aggregation->aggregations->add($aggregation2);
+        $aggregation->addAggregation($aggregation2);
 
         $result = [
             'agg_test_agg' => [

Aggregation/NestedAggregationTest.php

@@ -16,9 +16,11 @@ use ONGR\ElasticsearchBundle\DSL\Aggregation\NestedAggregation;
 class NestedAggregationTest extends \PHPUnit_Framework_TestCase
 {
     /**
-     * Test for nested aggregation toArray() method.
+     * Test for nested aggregation toArray() method exception.
+     *
+     * @expectedException \LogicException
      */
-    public function testToArray()
+    public function testToArrayException()
     {
         $aggregation = new NestedAggregation('test_agg');
         $aggregation->setPath('test_path');
@@ -31,4 +33,35 @@ class NestedAggregationTest extends \PHPUnit_Framework_TestCase
 
         $this->assertEquals($expectedResult, $aggregation->toArray());
     }
+
+    /**
+     * Test for nested aggregation toArray() method exception.
+     */
+    public function testToArray()
+    {
+        $termMock = $this
+            ->getMockBuilder('ONGR\ElasticsearchBundle\DSL\Aggregation\TermsAggregation')
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $termMock
+            ->expects($this->once())
+            ->method('toArray')
+            ->will($this->returnValue(['terms' => []]));
+
+        $aggregation = new NestedAggregation('test_nested_agg');
+        $aggregation->setPath('test_path');
+        $aggregation->addAggregation($termMock);
+
+        $expectedResult = [
+            'agg_test_nested_agg' => [
+                'nested' => ['path' => 'test_path'],
+                'aggregations' => [
+                    'terms' => [],
+                ],
+            ],
+        ];
+
+        $this->assertEquals($expectedResult, $aggregation->toArray());
+    }
 }

Aggregation/RangeAggregationTest.php

@@ -88,7 +88,7 @@ class RangeAggregationTest extends \PHPUnit_Framework_TestCase
         $aggregation2 = new RangeAggregation('test_agg_2');
         $aggregation2->addRange('20', '20');
 
-        $aggregation->aggregations->add($aggregation2);
+        $aggregation->addAggregation($aggregation2);
 
         $result = [
             'agg_test_agg' => [