diff --git a/Dockerfile b/Dockerfile
index 8a54b42..917e826 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,10 +1,13 @@
 FROM php:5.6-cli
 
-RUN docker-php-ext-install mbstring && \
-    curl -s https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
+RUN apt-get update && apt-get install -y zip unzip gzip libc6 php5-xdebug --no-install-recommends && rm -r /var/lib/apt/lists/*
 
-ADD . /opt/graze/dataFlow
+RUN docker-php-ext-install mbstring \
+    && curl -s https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer \
+    && echo "zend_extension=$(find / -name xdebug.so)" > /usr/local/etc/php/conf.d/xdebug.ini
 
-WORKDIR /opt/graze/dataFlow
+ADD . /opt/graze/dataNode
+
+WORKDIR /opt/graze/dataNode
 
 CMD /bin/bash
diff --git a/README.md b/README.md
index 145b4ef..3b54940 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,7 @@ Please see [CONTRIBUTING](CONTRIBUTING.md) for details.
 
 ## Security
 
-If you discover any security related issues, please email harry.bragg@graze.com instead of using the issue tracker.
+If you discover any security related issues, please email security@graze.com instead of using the issue tracker.
 
 ## Credits
 
diff --git a/src/NodeCollection.php b/src/NodeCollection.php
index 9377d2c..6029e6d 100644
--- a/src/NodeCollection.php
+++ b/src/NodeCollection.php
@@ -15,7 +15,7 @@
 class NodeCollection extends Collection implements NodeCollectionInterface
 {
     /**
-     * {@inheritdoc}
+     * @inheritdoc
      */
     public function add($value)
     {
@@ -26,9 +26,9 @@ public function add($value)
     }
 
     /**
-     * {@inheritdoc}
+     * @inheritdoc
      */
-    public function apply($fn)
+    public function apply(callable $fn)
     {
         foreach ($this->items as &$item) {
             $out = call_user_func($fn, $item);
@@ -67,10 +67,7 @@ public function getClone()
     }
 
     /**
-     * @param callable   $fn
-     * @param mixed|null $default
-     *
-     * @return NodeInterface|null
+     * @inheritdoc
      */
     public function first(callable $fn = null, $default = null)
     {
@@ -88,10 +85,7 @@ public function first(callable $fn = null, $default = null)
     }
 
     /**
-     * @param callable   $fn
-     * @param mixed|null $default
-     *
-     * @return NodeInterface|null
+     * @inheritdoc
      */
     public function last(callable $fn = null, $default = null)
     {
diff --git a/src/NodeCollectionInterface.php b/src/NodeCollectionInterface.php
index 6b46fce..d55a2ca 100644
--- a/src/NodeCollectionInterface.php
+++ b/src/NodeCollectionInterface.php
@@ -11,19 +11,19 @@ interface NodeCollectionInterface extends CollectionInterface, NodeInterface
      *
      * @return NodeCollectionInterface
      */
-    public function apply($fn);
+    public function apply(callable $fn);
 
     /**
-     * @param callable      $fn
-     * @param NodeInterface $default
+     * @param callable|null      $fn
+     * @param NodeInterface|null $default
      *
      * @return NodeInterface|null
      */
     public function first(callable $fn = null, $default = null);
 
     /**
-     * @param callable      $fn
-     * @param NodeInterface $default
+     * @param callable|null      $fn
+     * @param NodeInterface|null $default
      *
      * @return NodeInterface|null
      */
diff --git a/tests/unit/NodeCollectionTest.php b/tests/unit/NodeCollectionTest.php
index b654cdc..67831c7 100644
--- a/tests/unit/NodeCollectionTest.php
+++ b/tests/unit/NodeCollectionTest.php
@@ -6,6 +6,7 @@
 use Graze\DataNode\NodeInterface;
 use Graze\DataNode\Test\TestCase;
 use Graze\DataStructure\Collection\Collection;
+use InvalidArgumentException;
 use Mockery as m;
 
 class NodeCollectionTest extends TestCase
@@ -26,10 +27,7 @@ public function testAddingANonDataNodeWillThrowAnException()
     {
         $node = m::mock('Graze\Extensible\ExtensibleInterface');
 
-        static::setExpectedException(
-            'InvalidArgumentException',
-            "The specified value does not implement NodeInterface"
-        );
+        $this->expectException(InvalidArgumentException::class);
 
         $collection = new NodeCollection();
         $collection->add($node);
@@ -45,7 +43,7 @@ public function testCallingApplyWillModifyTheContentsUsingReference()
         $collection = new NodeCollection();
         $collection->add($node);
 
-        $collection->apply(function (&$item) {
+        $collection->apply(function ($item) {
             $item->someMethod();
         });
 
@@ -96,13 +94,16 @@ public function testFirstWithCallbackWillReturnTheFirstThatMatches()
     {
         $first = m::mock(NodeInterface::class);
         $second = m::mock(NodeInterface::class);
+        $third = m::mock(NodeInterface::class);
 
         $first->shouldReceive('thisOne')
               ->andReturn(false);
         $second->shouldReceive('thisOne')
                ->andReturn(true);
+        $third->shouldReceive('thosOne')
+              ->andReturn(true);
 
-        $collection = new NodeCollection([$first, $second]);
+        $collection = new NodeCollection([$first, $second, $third]);
 
         static::assertSame($second, $collection->first(function ($item) {
             return $item->thisOne();
@@ -113,15 +114,18 @@ public function testLastWithCallbackWillReturnTheFirstThatMatches()
     {
         $first = m::mock(NodeInterface::class);
         $second = m::mock(NodeInterface::class);
+        $third = m::mock(NodeInterface::class);
 
         $first->shouldReceive('thisOne')
               ->andReturn(true);
         $second->shouldReceive('thisOne')
-               ->andReturn(false);
+               ->andReturn(true);
+        $third->shouldReceive('thisOne')
+              ->andReturn(false);
 
-        $collection = new NodeCollection([$first, $second]);
+        $collection = new NodeCollection([$first, $second, $third]);
 
-        static::assertSame($first, $collection->last(function ($item) {
+        static::assertSame($second, $collection->last(function ($item) {
             return $item->thisOne();
         }));
     }
@@ -147,7 +151,7 @@ public function testFirstWithCallbackWillReturnDefaultIfNoMatchesAreFound()
         }));
     }
 
-    public function tesLastWithCallbackWillReturnDefaultIfNoMatchesAreFound()
+    public function testLastWithCallbackWillReturnDefaultIfNoMatchesAreFound()
     {
         $first = m::mock(NodeInterface::class);
         $second = m::mock(NodeInterface::class);
@@ -167,4 +171,25 @@ public function tesLastWithCallbackWillReturnDefaultIfNoMatchesAreFound()
             return $item->thisOne();
         }));
     }
+
+    public function testCloneWillCloneTheChildObjects()
+    {
+        $first = m::mock(NodeInterface::class);
+        $second = m::mock(NodeInterface::class);
+
+        $collection = new NodeCollection([$first, $second]);
+        $collection2 = $collection->getClone();
+
+        static::assertNotSame($collection, $collection2);
+        static::assertEquals($collection->count(), $collection2->count());
+        for ($i = 0; $i < $collection->count(); $i++) {
+            static::assertNotSame($collection->getAll()[$i], $collection2->getAll()[$i]);
+        }
+    }
+
+    public function testToString()
+    {
+        $collection = new NodeCollection();
+        static::assertEquals("NodeCollection", "$collection");
+    }
 }