diff --git a/.gitignore b/.gitignore
index dc48fa8..dddbbe4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,3 +8,4 @@ build
 composer.lock
 nbproject/*
 .idea
+phpunit.phar
diff --git a/composer.json b/composer.json
index bc541bc..0c68194 100644
--- a/composer.json
+++ b/composer.json
@@ -14,10 +14,14 @@
     },
     "autoload": {
         "psr-0": {
-            "Mailgun\\Tests": "tests/",
             "Mailgun": "src/"
         }
     },
+    "autoload-dev": {
+        "psr-4": {
+            "Mailgun\\Tests\\": "tests/"
+        }
+    },
     "license": "MIT",
     "authors": [
         {
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 33cea16..8707107 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit bootstrap="tests/Bootstrap.php"
+<phpunit bootstrap="vendor/autoload.php"
          colors="true"
          processIsolation="false"
          stopOnFailure="false"
@@ -11,7 +11,7 @@
 
     <testsuites>
         <testsuite>
-            <directory>tests/Mailgun/Tests</directory>
+            <directory>tests</directory>
         </testsuite>
     </testsuites>
 
diff --git a/src/Mailgun/Connection/RestClient.php b/src/Mailgun/Connection/RestClient.php
index c93d663..af1dfe3 100644
--- a/src/Mailgun/Connection/RestClient.php
+++ b/src/Mailgun/Connection/RestClient.php
@@ -119,8 +119,10 @@ class RestClient
         foreach ($fields as $fieldName) {
             if (isset($files[$fieldName])) {
                 if (is_array($files[$fieldName])) {
+                    $fileIndex = 0;
                     foreach ($files[$fieldName] as $file) {
-                        $postFiles[] = $this->prepareFile($fieldName, $file);
+                        $postFiles[] = $this->prepareFile($fieldName, $file, $fileIndex);
+                        $fileIndex++;
                     }
                 } else {
                     $postFiles[] = $this->prepareFile($fieldName, $files[$fieldName]);
@@ -251,10 +253,11 @@ class RestClient
      *
      * @param string       $fieldName
      * @param string|array $filePath
+     * @param integer      $fileIndex
      *
      * @return array
      */
-    protected function prepareFile($fieldName, $filePath)
+    protected function prepareFile($fieldName, $filePath, $fileIndex=0)
     {
         $filename = null;
         // Backward compatibility code
@@ -268,6 +271,9 @@ class RestClient
             $filePath = substr($filePath, 1);
         }
 
+        // Add index for multiple file support
+        $fieldName .= '[' . $fileIndex . ']';
+
         return [
             'name'     => $fieldName,
             'contents' => fopen($filePath, 'r'),
diff --git a/tests/Bootstrap.php b/tests/Bootstrap.php
deleted file mode 100644
index 95f8179..0000000
--- a/tests/Bootstrap.php
+++ /dev/null
@@ -1,4 +0,0 @@
-<?php
-
-//Grab the composer Autoloader!
-$autoloader = include dirname(__DIR__).'/vendor/autoload.php';
diff --git a/tests/Functional/InlineFileTest.php b/tests/Functional/InlineFileTest.php
new file mode 100644
index 0000000..0942f27
--- /dev/null
+++ b/tests/Functional/InlineFileTest.php
@@ -0,0 +1,51 @@
+<?php
+
+namespace Mailgun\Tests\Functional;
+
+/**
+ *
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+class InlineFileTest extends \PHPUnit_Framework_TestCase
+{
+    public function testSimpleExample()
+    {
+        // Create a Closure that validates the $files parameter to RestClient::send()
+        $fileValidator = function($files) {
+            // Validate standard params
+            $this->assertContains(['name'=>'from',    'contents'=>'bob@example.com'], $files);
+            $this->assertContains(['name'=>'to',      'contents'=>'alice@example.com'], $files);
+            $this->assertContains(['name'=>'subject', 'contents'=>'Foo'], $files);
+            $this->assertContains(['name'=>'text',    'contents'=>'Bar'], $files);
+
+            $fileNames = [
+                ['name'=>'inline[0]', 'filename'=>'foo.png'],
+                ['name'=>'inline[1]', 'filename'=>'bar.png']
+            ];
+            foreach ($fileNames as $idx => $fileName) {
+                foreach ($files as $file) {
+                    if ($file['name'] === $fileName['name'] && $file['filename'] === $fileName['filename']) {
+                        unset ($fileNames[$idx]);
+                        break;
+                    }
+                }
+            }
+
+            $this->assertEmpty($fileNames, 'Filenames could not be found');
+        };
+
+        // Create the mocked mailgun client. We use $this->assertEquals on $method, $uri and $body parameters.
+        $mailgun = MockedMailgun::create($this, 'POST', 'domain/messages', [], $fileValidator);
+
+        $builder = $mailgun->MessageBuilder();
+        $builder->setFromAddress("bob@example.com");
+        $builder->addToRecipient("alice@example.com");
+        $builder->setSubject("Foo");
+        $builder->setTextBody("Bar");
+
+        $builder->addInlineImage("@./tests/TestAssets/mailgun_icon1.png", 'foo.png');
+        $builder->addInlineImage("@./tests/TestAssets/mailgun_icon2.png", 'bar.png');
+
+        $mailgun->post("domain/messages", $builder->getMessage(), $builder->getFiles());
+    }
+}
diff --git a/tests/Mailgun/Tests/Functional/MockedMailgun.php b/tests/Functional/MockedMailgun.php
similarity index 100%
rename from tests/Mailgun/Tests/Functional/MockedMailgun.php
rename to tests/Functional/MockedMailgun.php
diff --git a/tests/Mailgun/Tests/Functional/MockedRestClient.php b/tests/Functional/MockedRestClient.php
similarity index 100%
rename from tests/Mailgun/Tests/Functional/MockedRestClient.php
rename to tests/Functional/MockedRestClient.php
diff --git a/tests/Functional/NoSamePostNameTest.php b/tests/Functional/NoSamePostNameTest.php
new file mode 100644
index 0000000..0f346ff
--- /dev/null
+++ b/tests/Functional/NoSamePostNameTest.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Mailgun\Tests\Functional;
+
+/**
+ *
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+class NoSamePostNameTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * No post names should ever be the same
+     */
+    public function testNames()
+    {
+        $fileValidator = function($files) {
+            $usedNames = [];
+            foreach ($files as $file) {
+                $this->assertFalse(in_array($file['name'], $usedNames), 'No files should have the same POST name.');
+                $usedNames[] = $file['name'];
+            }
+        };
+
+        // Create the mocked mailgun client. We use $this->assertEquals on $method, $uri and $body parameters.
+        $mailgun = MockedMailgun::create($this, 'POST', 'domain/messages', [], $fileValidator);
+
+        $builder = $mailgun->MessageBuilder();
+        $builder->setFromAddress("bob@example.com");
+        $builder->addToRecipient("alice@example.com");
+        $builder->setSubject("Foo");
+        $builder->setTextBody("Bar");
+
+        $builder->addAttachment("@./tests/TestAssets/mailgun_icon1.png", 'foo.png');
+        $builder->addAttachment("@./tests/TestAssets/mailgun_icon1.png", 'foo.png');
+        $builder->addInlineImage("@./tests/TestAssets/mailgun_icon2.png", 'bar.png');
+        $builder->addInlineImage("@./tests/TestAssets/mailgun_icon2.png", 'bar.png');
+
+        $mailgun->post("domain/messages", $builder->getMessage(), $builder->getFiles());
+    }
+}
diff --git a/tests/Mailgun/Tests/Functional/SendMessageTest.php b/tests/Functional/SendMessageTest.php
similarity index 99%
rename from tests/Mailgun/Tests/Functional/SendMessageTest.php
rename to tests/Functional/SendMessageTest.php
index 193a2bf..4966920 100644
--- a/tests/Mailgun/Tests/Functional/SendMessageTest.php
+++ b/tests/Functional/SendMessageTest.php
@@ -27,5 +27,5 @@ class SendMessageTest extends \PHPUnit_Framework_TestCase
             'to'      => 'alice@example.com',
             'subject' => 'Foo',
             'text'    => 'Bar'));
-        }
+    }
 }
diff --git a/tests/Mailgun/Tests/Lists/OptInHandlerTest.php b/tests/Lists/OptInHandlerTest.php
similarity index 100%
rename from tests/Mailgun/Tests/Lists/OptInHandlerTest.php
rename to tests/Lists/OptInHandlerTest.php
diff --git a/tests/Mailgun/Tests/TestAssets/mailgun_icon.png b/tests/Mailgun/Tests/TestAssets/mailgun_icon.png
deleted file mode 100644
index 604f673..0000000
Binary files a/tests/Mailgun/Tests/TestAssets/mailgun_icon.png and /dev/null differ
diff --git a/tests/Mailgun/Tests/TestAssets/rackspace_logo.jpg b/tests/Mailgun/Tests/TestAssets/rackspace_logo.jpg
deleted file mode 100644
index 46360a0..0000000
Binary files a/tests/Mailgun/Tests/TestAssets/rackspace_logo.jpg and /dev/null differ
diff --git a/tests/Mailgun/Tests/MailgunTest.php b/tests/MailgunTest.php
similarity index 97%
rename from tests/Mailgun/Tests/MailgunTest.php
rename to tests/MailgunTest.php
index 204d2f5..5c7e305 100644
--- a/tests/Mailgun/Tests/MailgunTest.php
+++ b/tests/MailgunTest.php
@@ -1,6 +1,6 @@
 <?PHP
 
-namespace Mailgun\Tests\Lists;
+namespace Mailgun\Tests;
 
 use Mailgun\Mailgun;
 
diff --git a/tests/Mailgun/Tests/MailgunTestCase.php b/tests/MailgunTestCase.php
similarity index 100%
rename from tests/Mailgun/Tests/MailgunTestCase.php
rename to tests/MailgunTestCase.php
diff --git a/tests/Mailgun/Tests/Messages/BatchMessageTest.php b/tests/Messages/BatchMessageTest.php
similarity index 100%
rename from tests/Mailgun/Tests/Messages/BatchMessageTest.php
rename to tests/Messages/BatchMessageTest.php
diff --git a/tests/Messages/ComplexMessageTest.php b/tests/Messages/ComplexMessageTest.php
new file mode 100644
index 0000000..c2a1b54
--- /dev/null
+++ b/tests/Messages/ComplexMessageTest.php
@@ -0,0 +1,111 @@
+<?PHP
+
+namespace Mailgun\Tests\Messages;
+
+use Mailgun\Tests\Mock\Mailgun;
+use Mailgun\Connection\RestClient;
+
+
+class mockRestClient extends RestClient{
+  public function send($method, $uri, $body = null, $files = [], array $headers = [])
+  {
+      $result = new \stdClass;
+
+      $result->method = $method;
+      $result->uri = $uri;
+      $result->body = $body;
+      $result->files = $files;
+      $result->headers = $headers;
+
+      return $result;
+  }
+}
+
+class mockMailgun extends Mailgun{
+  public function __construct(
+      $apiKey = null,
+      HttpClient $httpClient = null,
+      $apiEndpoint = 'api.mailgun.net'
+  ) {
+      $this->apiKey = $apiKey;
+      $this->restClient = new mockRestClient($apiKey, $apiEndpoint, $httpClient);
+  }
+}
+
+class ComplexMessageTest extends \Mailgun\Tests\MailgunTestCase
+{
+    private $client;
+    private $sampleDomain = 'samples.mailgun.org';
+
+    public function setUp()
+    {
+        $this->client = new mockMailgun('My-Super-Awesome-API-Key');
+    }
+
+    public function testSendComplexMessage()
+    {
+
+        $message = [
+          'to' => 'test@test.mailgun.org',
+          'from'    => 'sender@test.mailgun.org',
+          'subject' => 'This is my test subject',
+          'text'    => 'Testing!'
+        ];
+
+        $files = [
+            'inline' => [
+              [
+                'remoteName'=> 'mailgun_icon1.png',
+                'filePath' => 'tests/TestAssets/mailgun_icon1.png'
+              ],
+              [
+                'remoteName'=> 'mailgun_icon2.png',
+                'filePath' => 'tests/TestAssets/mailgun_icon2.png'
+              ]
+            ]
+        ];
+
+        $result = $this->client->sendMessage('test.mailgun.org', $message, $files);
+
+        $this->assertEquals('POST', $result->method);
+        $this->assertEquals('test.mailgun.org/messages', $result->uri);
+        $this->assertEquals([], $result->body);
+
+        // Start a counter, make sure all files are asserted
+        $testCount = 0;
+
+        foreach($result->files as $file){
+          if ($file['name'] == 'to'){
+            $this->assertEquals($file['contents'], 'test@test.mailgun.org');
+            $testCount++;
+          }
+          if ($file['name'] == 'from'){
+            $this->assertEquals($file['contents'], 'sender@test.mailgun.org');
+            $testCount++;
+          }
+          if ($file['name'] == 'subject'){
+            $this->assertEquals($file['contents'], 'This is my test subject');
+            $testCount++;
+          }
+          if ($file['name'] == 'text'){
+            $this->assertEquals($file['contents'], 'Testing!');
+            $testCount++;
+          }
+          if ($file['name'] == 'inline[0]'){
+            $this->assertEquals($file['filename'], 'mailgun_icon1.png');
+            $testCount++;
+          }
+          if ($file['name'] == 'inline[1]'){
+            $this->assertEquals($file['filename'], 'mailgun_icon2.png');
+            $testCount++;
+          }
+        }
+
+        // Make sure all "files" are asserted
+        $this->assertEquals(count($result->files), $testCount);
+
+        $this->assertEquals([], $result->body);
+        $this->assertEquals([], $result->headers);
+
+    }
+}
diff --git a/tests/Mailgun/Tests/Messages/MessageBuilderTest.php b/tests/Messages/MessageBuilderTest.php
similarity index 100%
rename from tests/Mailgun/Tests/Messages/MessageBuilderTest.php
rename to tests/Messages/MessageBuilderTest.php
diff --git a/tests/Mailgun/Tests/Messages/StandardMessageTest.php b/tests/Messages/StandardMessageTest.php
similarity index 100%
rename from tests/Mailgun/Tests/Messages/StandardMessageTest.php
rename to tests/Messages/StandardMessageTest.php
diff --git a/tests/Mailgun/Tests/Mock/Connection/TestBroker.php b/tests/Mock/Connection/TestBroker.php
similarity index 100%
rename from tests/Mailgun/Tests/Mock/Connection/TestBroker.php
rename to tests/Mock/Connection/TestBroker.php
diff --git a/tests/Mailgun/Tests/Mock/Mailgun.php b/tests/Mock/Mailgun.php
similarity index 100%
rename from tests/Mailgun/Tests/Mock/Mailgun.php
rename to tests/Mock/Mailgun.php
diff --git a/tests/Mailgun/Tests/TestAssets/mailgun_icon1.png b/tests/TestAssets/mailgun_icon1.png
similarity index 100%
rename from tests/Mailgun/Tests/TestAssets/mailgun_icon1.png
rename to tests/TestAssets/mailgun_icon1.png
diff --git a/tests/Mailgun/Tests/TestAssets/mailgun_icon2.png b/tests/TestAssets/mailgun_icon2.png
similarity index 100%
rename from tests/Mailgun/Tests/TestAssets/mailgun_icon2.png
rename to tests/TestAssets/mailgun_icon2.png