Merge branch '2.8' into 3.1

* 2.8:
  [travis] fix after box updates
  Console: Fix indentation of Help: section of txt usage help
  [Intl] Update ICU data to 57.1
  [Config] Improved test
  Added class existence check if is_subclass_of() fails in compiler passes

Tests/Definition/ArrayNodeTest.php

@@ -173,4 +173,41 @@ public function getPreNormalizedNormalizedOrderedData()
             ),
         );
     }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage Child nodes must be named.
+     */
+    public function testAddChildEmptyName()
+    {
+        $node = new ArrayNode('root');
+
+        $childNode = new ArrayNode('');
+        $node->addChild($childNode);
+    }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage A child node named "foo" already exists.
+     */
+    public function testAddChildNameAlreadyExists()
+    {
+        $node = new ArrayNode('root');
+
+        $childNode = new ArrayNode('foo');
+        $node->addChild($childNode);
+
+        $childNodeWithSameName = new ArrayNode('foo');
+        $node->addChild($childNodeWithSameName);
+    }
+
+    /**
+     * @expectedException \RuntimeException
+     * @expectedExceptionMessage The node at path "foo" has no default value.
+     */
+    public function testGetDefaultValueWithoutDefaultValue()
+    {
+        $node = new ArrayNode('foo');
+        $node->getDefaultValue();
+    }
 }