minor #19476 [Config] Improved test (zomberg)

This PR was merged into the 2.7 branch.

Discussion
----------

[Config] Improved test

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

Commits
-------

456d53a [Config] Improved test

src/Symfony/Component/Config/Tests/Definition/ArrayNodeTest.php

@@ -161,4 +161,41 @@ class ArrayNodeTest extends \PHPUnit_Framework_TestCase
             ),
         );
     }
+
+    /**
+     * @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();
+    }
 }