Adds "Element::isValid" method for checking element presence in DOM

src/Behat/Mink/Element/Element.php

@@ -54,6 +54,16 @@ public function has($selector, $locator)
         return null !== $this->find($selector, $locator);
     }
 
+    /**
+     * Checks if an element is still valid.
+     *
+     * @return boolean
+     */
+    public function isValid()
+    {
+        return 1 === count($this->getSession()->getDriver()->find($this->getXpath()));
+    }
+
     /**
      * Finds first element with specified selector.
      *

src/Behat/Mink/Element/ElementInterface.php

@@ -43,6 +43,13 @@ public function getSession();
      */
     public function has($selector, $locator);
 
+    /**
+     * Checks if an element is still valid.
+     *
+     * @return boolean
+     */
+    public function isValid();
+
     /**
      * Finds first element with specified selector.
      *

tests/Behat/Mink/Element/NodeElementTest.php

@@ -34,6 +34,34 @@ public function testGetText()
         $this->assertEquals($expected, $node->getText());
     }
 
+    public function testElementIsValid()
+    {
+        $elementXpath = 'some xpath';
+        $node = new NodeElement($elementXpath, $this->session);
+
+        $this->session->getDriver()
+            ->expects($this->once())
+            ->method('find')
+            ->with($elementXpath)
+            ->will($this->returnValue(array($elementXpath)));
+
+        $this->assertTrue($node->isValid());
+    }
+
+    public function testElementIsNotValid()
+    {
+        $node = new NodeElement('some xpath', $this->session);
+
+        $this->session->getDriver()
+            ->expects($this->exactly(2))
+            ->method('find')
+            ->with('some xpath')
+            ->will($this->onConsecutiveCalls(array(), array('xpath1', 'xpath2')));
+
+        $this->assertFalse($node->isValid(), 'no elements found is invalid element');
+        $this->assertFalse($node->isValid(), 'more then 1 element found is invalid element');
+    }
+
     public function testHasAttribute()
     {
         $node = new NodeElement('input_tag', $this->session);