diff --git a/tests/Lists/OptInHandlerTest.php b/tests/Lists/OptInHandlerTest.php
index 754c72a..5073193 100644
--- a/tests/Lists/OptInHandlerTest.php
+++ b/tests/Lists/OptInHandlerTest.php
@@ -14,7 +14,7 @@ use Mailgun\Tests\Mock\Mailgun;
 class OptInHandlerTest extends \Mailgun\Tests\MailgunTestCase
 {
     private $client;
-    private $sampleDomain = 'samples.mailgun.org';
+
     private $optInHandler;
 
     public function setUp()
diff --git a/tests/Messages/ComplexMessageTest.php b/tests/Messages/ComplexMessageTest.php
index c828a07..af60270 100644
--- a/tests/Messages/ComplexMessageTest.php
+++ b/tests/Messages/ComplexMessageTest.php
@@ -43,7 +43,6 @@ class mockMailgun extends Mailgun
 class ComplexMessageTest extends \Mailgun\Tests\MailgunTestCase
 {
     private $client;
-    private $sampleDomain = 'samples.mailgun.org';
 
     public function setUp()
     {
diff --git a/tests/Messages/StandardMessageTest.php b/tests/Messages/StandardMessageTest.php
index 9336c54..87a954b 100644
--- a/tests/Messages/StandardMessageTest.php
+++ b/tests/Messages/StandardMessageTest.php
@@ -14,7 +14,6 @@ use Mailgun\Tests\Mock\Mailgun;
 class StandardMessageTest extends \Mailgun\Tests\MailgunTestCase
 {
     private $client;
-    private $sampleDomain = 'samples.mailgun.org';
 
     public function setUp()
     {