diff --git a/src/Document.php b/src/Document.php
index ceb78d1..f7deb9c 100644
--- a/src/Document.php
+++ b/src/Document.php
@@ -32,7 +32,8 @@ public function addIncluded($link)
 
         foreach ($resources as $k => $resource) {
             foreach ($this->included as $includedResource) {
-                if ($includedResource->getType() === $resource->getType() && $includedResource->getId() === $resource->getId()) {
+                if ($includedResource->getType() === $resource->getType()
+                    && $includedResource->getId() === $resource->getId()) {
                     $includedResource->merge($resource);
                     unset($resources[$k]);
                     break;
@@ -125,7 +126,7 @@ public function __toString()
     {
         return json_encode($this->toArray());
     }
-    
+
     public function jsonSerialize()
     {
         return $this->toArray();
diff --git a/src/SerializerAbstract.php b/src/SerializerAbstract.php
index ea3c9c3..73c869e 100644
--- a/src/SerializerAbstract.php
+++ b/src/SerializerAbstract.php
@@ -116,8 +116,7 @@ public function resource($data)
                     );
                 }
 
-                if ($method && $element)
-                     {
+                if ($method && $element) {
                     if (! ($element instanceof Relationship)) {
                         $element = new Relationship($element);
                     }
diff --git a/tests/CriteriaTest.php b/tests/CriteriaTest.php
new file mode 100644
index 0000000..816810a
--- /dev/null
+++ b/tests/CriteriaTest.php
@@ -0,0 +1,62 @@
+<?php namespace Tobscure\JsonApi;
+
+use Tobscure\JsonApi\Criteria;
+
+class CriteriaTest extends \PHPUnit_Framework_TestCase
+{
+    public function testGetIncludeReturnsArrayOfIncludes()
+    {
+        $criteria = new Criteria(['include' => 'posts,images']);
+
+        $this->assertEquals(['posts', 'images'], $criteria->getInclude());
+    }
+
+    public function testGetSortReturnsArrayOfFieldToSortDirection()
+    {
+        $criteria = new Criteria(['sort' => '+firstname']);
+
+        $this->assertEquals(['firstname' => 'asc'], $criteria->getSort());
+    }
+
+    public function testGetSortSupportsMultipleSortedFieldsSeparatedByComma()
+    {
+        $criteria = new Criteria(['sort' => '+firstname,-lastname']);
+
+        $this->assertEquals(['firstname' => 'asc', 'lastname' => 'desc'], $criteria->getSort());
+    }
+
+    public function testGetSortIgnoresInvalidDirections()
+    {
+        $criteria = new Criteria(['sort' => '*firstname']);
+
+        $this->assertEmpty($criteria->getSort());
+    }
+
+    public function testGetSortDefaultsToEmptyArray()
+    {
+        $criteria = new Criteria([]);
+
+        $this->assertEmpty($criteria->getSort());
+    }
+
+    public function testGetOffsetParsesThePageOffset()
+    {
+        $criteria = new Criteria(['page' => ['offset' => 10]]);
+
+        $this->assertEquals(10, $criteria->getOffset());
+    }
+
+    public function testGetOffsetIsAtLeastZero()
+    {
+        $criteria = new Criteria(['page' => ['offset' => -5]]);
+
+        $this->assertEquals(0, $criteria->getOffset());
+    }
+
+    public function testGetLimitParsesThePageLimit()
+    {
+        $criteria = new Criteria(['page' => ['limit' => 100]]);
+
+        $this->assertEquals(100, $criteria->getLimit());
+    }
+}
diff --git a/tests/DocumentTest.php b/tests/DocumentTest.php
new file mode 100644
index 0000000..48b2b59
--- /dev/null
+++ b/tests/DocumentTest.php
@@ -0,0 +1,21 @@
+<?php namespace Tobscure\JsonApi;
+
+use Tobscure\JsonApi\Document;
+use Tobscure\JsonApi\Elements\Resource;
+
+class DocumentTest extends \PHPUnit_Framework_TestCase
+{
+    public function testToArrayIncludesTheResourcesRepresentation()
+    {
+        $resource = new Resource('post', 1);
+        $document = new Document();
+        $document->setData($resource);
+
+        $this->assertEquals(['data' => $resource->toArray()], $document->toArray());
+    }
+
+    public function testItCanBeSerializedToJson()
+    {
+        $this->assertEquals('[]', (string) new Document());
+    }
+}
diff --git a/tests/Elements/CollectionTest.php b/tests/Elements/CollectionTest.php
new file mode 100644
index 0000000..35c89cd
--- /dev/null
+++ b/tests/Elements/CollectionTest.php
@@ -0,0 +1,25 @@
+<?php namespace Tobscure\JsonApi\Elements;
+
+use Tobscure\JsonApi\Elements\Collection;
+use Tobscure\JsonApi\Elements\Resource;
+
+class CollectionTest extends \PHPUnit_Framework_TestCase
+{
+    public function testToArrayReturnsArrayOfResources()
+    {
+        $post1 = new Resource('post', 1);
+        $post2 = new Resource('post', 2);
+        $collection = new Collection('post', [$post1, $post2]);
+
+        $this->assertEquals([$post1->toArray(), $post2->toArray()], $collection->toArray());
+    }
+
+    public function testGetIdReturnsArrayOfResourceIds()
+    {
+        $post1 = new Resource('post', 1);
+        $post2 = new Resource('post', 2);
+        $collection = new Collection('post', [$post1, $post2]);
+
+        $this->assertEquals([1, 2], $collection->getId());
+    }
+}