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());
+    }
+}