diff --git a/.travis.yml b/.travis.yml
index 7982182..495a677 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,20 +1,19 @@
 language: php
 
 php:
-  - 5.4
-  - 5.5
-  - 5.6
+  - 7.0
+  - 7.1
+  - 7.2
+  - 7.3
+  - 7.4
+  - nightly
   - hhvm
 
-env:
-  - GUZZLE_VERSION="5.1.0"
-
-before_script: composer install
-
 install:
-  - composer require guzzlehttp/guzzle:${GUZZLE_VERSION}
+  - travis_retry composer update --no-interaction --prefer-source
 
 matrix:
   allow_failures:
     - php: hhvm
+    - php: nightly
   fast_finish: true
\ No newline at end of file
diff --git a/composer.json b/composer.json
index 8bc7064..b466911 100755
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,7 @@
         "guzzlehttp/guzzle": "^5.1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "4.4.1"
+        "phpunit/phpunit": "^7.0|^6.0"
     },
     "authors": [
         {
diff --git a/test/Auth/CtctOAuth2UnitTest.php b/test/Auth/CtctOAuth2UnitTest.php
index 70d9c82..fdd8c12 100644
--- a/test/Auth/CtctOAuth2UnitTest.php
+++ b/test/Auth/CtctOAuth2UnitTest.php
@@ -7,7 +7,7 @@
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Subscriber\Mock;
 
-class CtctOAuth2UnitTest extends PHPUnit_Framework_TestCase
+class CtctOAuth2UnitTest extends \PHPUnit\Framework\TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/AccountServiceUnitTest.php b/test/Services/AccountServiceUnitTest.php
index 7f51d6d..d81d23a 100644
--- a/test/Services/AccountServiceUnitTest.php
+++ b/test/Services/AccountServiceUnitTest.php
@@ -6,8 +6,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class AccountServiceUnitTest extends PHPUnit_Framework_TestCase
+class AccountServiceUnitTest extends TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/ActivityServiceUnitTest.php b/test/Services/ActivityServiceUnitTest.php
index 8874639..f4da0ad 100644
--- a/test/Services/ActivityServiceUnitTest.php
+++ b/test/Services/ActivityServiceUnitTest.php
@@ -4,8 +4,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class ActivityServiceUnitTest extends PHPUnit_Framework_TestCase
+class ActivityServiceUnitTest extends TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/CampaignScheduleServiceUnitTest.php b/test/Services/CampaignScheduleServiceUnitTest.php
index 2cdbc6c..8e93233 100755
--- a/test/Services/CampaignScheduleServiceUnitTest.php
+++ b/test/Services/CampaignScheduleServiceUnitTest.php
@@ -8,8 +8,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class CampaignScheduleServiceUnitTest extends PHPUnit_Framework_TestCase
+class CampaignScheduleServiceUnitTest extends TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/CampaignTrackingServiceUnitTest.php b/test/Services/CampaignTrackingServiceUnitTest.php
index c3a3e20..59b1c2d 100755
--- a/test/Services/CampaignTrackingServiceUnitTest.php
+++ b/test/Services/CampaignTrackingServiceUnitTest.php
@@ -13,8 +13,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class CampaignTrackingServiceUnitTest extends PHPUnit_Framework_TestCase
+class CampaignTrackingServiceUnitTest extends TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/ContactServiceUnitTest.php b/test/Services/ContactServiceUnitTest.php
index 48cc217..37b3c86 100755
--- a/test/Services/ContactServiceUnitTest.php
+++ b/test/Services/ContactServiceUnitTest.php
@@ -8,8 +8,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class ContactServiceUnitTest extends PHPUnit_Framework_TestCase
+class ContactServiceUnitTest extends TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/ContactTrackingServiceUnitTest.php b/test/Services/ContactTrackingServiceUnitTest.php
index 36801bc..2dfd024 100755
--- a/test/Services/ContactTrackingServiceUnitTest.php
+++ b/test/Services/ContactTrackingServiceUnitTest.php
@@ -13,8 +13,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class ContactTrackingServiceUnitTest extends PHPUnit_Framework_TestCase
+class ContactTrackingServiceUnitTest extends TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/EmailCampaignServiceUnitTest.php b/test/Services/EmailCampaignServiceUnitTest.php
index ac2407e..f6aae5f 100755
--- a/test/Services/EmailCampaignServiceUnitTest.php
+++ b/test/Services/EmailCampaignServiceUnitTest.php
@@ -9,8 +9,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class EmailMarketingServiceUnitTest extends PHPUnit_Framework_TestCase
+class EmailMarketingServiceUnitTest extends TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/LibraryServiceUnitTest.php b/test/Services/LibraryServiceUnitTest.php
index fda7742..1efc520 100644
--- a/test/Services/LibraryServiceUnitTest.php
+++ b/test/Services/LibraryServiceUnitTest.php
@@ -9,8 +9,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class LibraryServiceUnitTest extends PHPUnit_Framework_TestCase
+class LibraryServiceUnitTest extends TestCase
 {
     /**
      * @var Client
diff --git a/test/Services/ListServiceUnitTest.php b/test/Services/ListServiceUnitTest.php
index 1073dd9..f515792 100755
--- a/test/Services/ListServiceUnitTest.php
+++ b/test/Services/ListServiceUnitTest.php
@@ -8,8 +8,9 @@
 use GuzzleHttp\Subscriber\Mock;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Message\Response;
+use PHPUnit\Framework\TestCase;
 
-class ListServiceUnitTest extends PHPUnit_Framework_TestCase
+class ListServiceUnitTest extends TestCase
 {
     /**
      * @var Client