diff --git a/composer.json b/composer.json
index 8f79aeb..bd0c9d8 100644
--- a/composer.json
+++ b/composer.json
@@ -22,7 +22,7 @@
         "ext-mbstring": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.7",
+        "phpunit/phpunit": "^5.7 || ^6.5",
         "sebastian/version": "^1.0.6",
         "squizlabs/php_codesniffer": "~2.0",
         "friendsofphp/php-cs-fixer": "^2.16"
diff --git a/test/phpunit.xml.dist b/test/phpunit.xml.dist
new file mode 100644
index 0000000..a3c0314
--- /dev/null
+++ b/test/phpunit.xml.dist
@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit colors="true" bootstrap="../vendor/autoload.php">
+    <testsuites>
+        <testsuite name="All">
+            <directory>.</directory>
+        </testsuite>
+    </testsuites>
+    <filter>
+        <whitelist processUncoveredFilesFromWhitelist="true">
+            <directory suffix=".php">../lib</directory>
+        </whitelist>
+    </filter>
+</phpunit>
diff --git a/test/unit/ClientTest.php b/test/unit/ClientTest.php
index 16e8d25..0e19748 100644
--- a/test/unit/ClientTest.php
+++ b/test/unit/ClientTest.php
@@ -2,10 +2,11 @@
 
 namespace SendGrid\Test;
 
+use PHPUnit\Framework\TestCase;
 use SendGrid\Client;
 use SendGrid\Exception\InvalidRequest;
 
-class ClientTest extends \PHPUnit_Framework_TestCase
+class ClientTest extends TestCase
 {
     /** @var MockClient */
     private $client;
diff --git a/test/unit/FilesExistTest.php b/test/unit/FilesExistTest.php
index 7b9fc09..8f9f928 100644
--- a/test/unit/FilesExistTest.php
+++ b/test/unit/FilesExistTest.php
@@ -2,7 +2,9 @@
 
 namespace SendGrid\Test;
 
-class FilesExistTest extends \PHPUnit_Framework_TestCase
+use PHPUnit\Framework\TestCase;
+
+class FilesExistTest extends TestCase
 {
     public function testFileArePresentInRepo()
     {
diff --git a/test/unit/LicenceYearTest.php b/test/unit/LicenceYearTest.php
index c6005e6..a4fa79b 100644
--- a/test/unit/LicenceYearTest.php
+++ b/test/unit/LicenceYearTest.php
@@ -2,7 +2,9 @@
 
 namespace SendGrid\Test;
 
-class LicenceYearTest extends \PHPUnit_Framework_TestCase
+use PHPUnit\Framework\TestCase;
+
+class LicenceYearTest extends TestCase
 {
     public function testConstructor()
     {
diff --git a/test/unit/ResponseTest.php b/test/unit/ResponseTest.php
index a4927ae..3366ec6 100644
--- a/test/unit/ResponseTest.php
+++ b/test/unit/ResponseTest.php
@@ -3,13 +3,14 @@
 namespace SendGrid\Test;
 
 use SendGrid\Response;
+use PHPUnit\Framework\TestCase;
 
-class ResponseTest extends \PHPUnit_Framework_TestCase
+class ResponseTest extends TestCase
 {
     public function testConstructor()
     {
         $response = new Response();
-        
+
         $this->assertAttributeEquals(200, 'statusCode', $response);
         $this->assertAttributeEquals('', 'body', $response);
         $this->assertAttributeEquals([], 'headers', $response);
@@ -41,11 +42,11 @@ public function testHeaders()
 
         $this->assertEquals(['Content-Type: text/html'], $response->headers());
     }
-    
+
     public function testAssociativeHeaders()
     {
         $response = new Response(null, null, ['Content-Type: text/html', 'HTTP/1.1 200 OK']);
-        
+
         $this->assertEquals(['Content-Type' => 'text/html', 'Status' => 'HTTP/1.1 200 OK'], $response->headers(true));
     }
 }