diff --git a/composer.json b/composer.json
index e56186c..a758d7e 100644
--- a/composer.json
+++ b/composer.json
@@ -15,10 +15,11 @@
         }
     ],
     "require": {
-        "omnipay/common": "~2.0"
+        "omnipay/common": "^3.0",
+      "ext-json": "*"
     },
     "require-dev": {
-        "omnipay/tests": "~2.0",
+        "omnipay/tests": "^3.0",
         "satooshi/php-coveralls": "^0.7.1"
     },
     "autoload": {
@@ -36,7 +37,8 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "1.0-dev"
+            "1.0.x-dev": "1.0-dev",
+            "dev-master": "3.0.x-dev"
         }
     }
-}
\ No newline at end of file
+}
diff --git a/src/Gateway.php b/src/Gateway.php
index 4d56e48..370a3f0 100644
--- a/src/Gateway.php
+++ b/src/Gateway.php
@@ -3,6 +3,13 @@
 namespace Omnipay\TwoCheckoutPlus;
 
 use Omnipay\Common\AbstractGateway;
+use Omnipay\Common\Message\AbstractRequest;
+use Omnipay\TwoCheckoutPlus\Message\PurchaseRequest;
+use Omnipay\TwoCheckoutPlus\Message\RefundRequest;
+use Omnipay\TwoCheckoutPlus\Message\DetailSaleRequest;
+use Omnipay\TwoCheckoutPlus\Message\StopRecurringRequest;
+use Omnipay\TwoCheckoutPlus\Message\CompletePurchaseRequest;
+use Omnipay\TwoCheckoutPlus\Message\NotificationRequest;
 
 /**
  * 2Checkout Gateway.
@@ -121,8 +128,6 @@ public function setLanguage($value)
     /**
      * Getter: purchase step.
      *
-     * @param $value
-     *
      * @return $this
      */
     public function getPurchaseStep()
@@ -387,45 +392,45 @@ public function setAdminPassword($value)
     /**
      * @param array $parameters
      *
-     * @return \Omnipay\Common\Message\AbstractRequest
+     * @return AbstractRequest
      */
     public function purchase(array $parameters = array())
     {
-        return $this->createRequest('\Omnipay\TwoCheckoutPlus\Message\PurchaseRequest', $parameters);
+        return $this->createRequest(PurchaseRequest::class, $parameters);
     }
 
     public function refund(array $parameters = array())
     {
-        return $this->createRequest('\Omnipay\TwoCheckoutPlus\Message\RefundRequest', $parameters);
+        return $this->createRequest(RefundRequest::class, $parameters);
     }
 
     public function fetchSaleDetails(array $parameters = array())
     {
-        return $this->createRequest('\Omnipay\TwoCheckoutPlus\Message\DetailSaleRequest', $parameters);
+        return $this->createRequest(DetailSaleRequest::class, $parameters);
     }
 
     public function stopRecurring(array $parameters = array())
     {
-        return $this->createRequest('\Omnipay\TwoCheckoutPlus\Message\StopRecurringRequest', $parameters);
+        return $this->createRequest(StopRecurringRequest::class, $parameters);
     }
 
     /**
      * @param array $parameters
      *
-     * @return \Omnipay\Common\Message\AbstractRequest
+     * @return AbstractRequest
      */
     public function completePurchase(array $parameters = array())
     {
-        return $this->createRequest('\Omnipay\TwoCheckoutPlus\Message\CompletePurchaseRequest', $parameters);
+        return $this->createRequest(CompletePurchaseRequest::class, $parameters);
     }
 
     /**
      * @param array $parameters
      *
-     * @return \Omnipay\Common\Message\AbstractRequest
+     * @return AbstractRequest
      */
     public function acceptNotification(array $parameters = array())
     {
-        return $this->createRequest('\Omnipay\TwoCheckoutPlus\Message\NotificationRequest', $parameters);
+        return $this->createRequest(NotificationRequest::class, $parameters);
     }
 }
diff --git a/src/Message/CompletePurchaseRequest.php b/src/Message/CompletePurchaseRequest.php
index 566e675..105bf40 100644
--- a/src/Message/CompletePurchaseRequest.php
+++ b/src/Message/CompletePurchaseRequest.php
@@ -36,7 +36,7 @@ public function getData()
         }
 
         $key = md5($this->getSecretWord().$this->getAccountNumber().$orderNo.$orderAmount);
-        if (strtolower($this->httpRequest->$request_type->get('key')) !== $key) {
+        if (!hash_equals($key, strtolower($this->httpRequest->$request_type->get('key')))) {
             throw new InvalidResponseException('Invalid key');
         }
 
diff --git a/src/Message/CompletePurchaseResponse.php b/src/Message/CompletePurchaseResponse.php
index 41eda3a..7b1c9b2 100644
--- a/src/Message/CompletePurchaseResponse.php
+++ b/src/Message/CompletePurchaseResponse.php
@@ -21,12 +21,12 @@ public function isSuccessful()
      */
     public function getTransactionReference()
     {
-        return isset($this->data['order_number']) ? $this->data['order_number'] : null;
+        return $this->data['order_number'] ?? null;
     }
 
     public function getTransactionInvoice()
     {
-        return isset($this->data['invoice_id']) ? $this->data['invoice_id'] : null;
+        return $this->data['invoice_id'] ?? null;
     }
 
     /**
@@ -36,6 +36,6 @@ public function getTransactionInvoice()
      */
     public function getTransactionId()
     {
-        return isset($this->data['merchant_order_id']) ? $this->data['merchant_order_id'] : null;
+        return $this->data['merchant_order_id'] ?? null;
     }
 }
diff --git a/src/Message/DetailSaleRequest.php b/src/Message/DetailSaleRequest.php
index 5257e4a..37a855c 100644
--- a/src/Message/DetailSaleRequest.php
+++ b/src/Message/DetailSaleRequest.php
@@ -2,7 +2,8 @@
 
 namespace Omnipay\TwoCheckoutPlus\Message;
 
-use Guzzle\Http\Exception\BadResponseException;
+use Omnipay\Common\Http\Exception\NetworkException;
+use Omnipay\Common\Http\Exception\RequestException;
 
 /**
  * Purchase Request.
@@ -31,21 +32,17 @@ public function getEndPoint()
      */
     public function getRequestHeaders()
     {
-        return array(
+        return [
             'Accept' => 'application/json',
-        );
-    }
-
-    public function isNotNull($value)
-    {
-        return !is_null($value);
+            'Authorization' => 'Basic ' . base64_encode($this->getAdminUsername() . ':' . $this->getAdminPassword())
+        ];
     }
 
     public function getData()
     {
         $this->validate('adminUsername', 'adminPassword');
 
-        $data = array();
+        $data = [];
         $data['admin_username'] = $this->getAdminUsername();
         $data['admin_password'] = $this->getAdminPassword();
 
@@ -58,7 +55,7 @@ public function getData()
         }
 
         $data = array_filter($data, function ($value) {
-            return !is_null($value);
+            return $value !== null;
         });
 
         // remove unwanted data
@@ -76,8 +73,7 @@ public function getData()
     public function sendData($data)
     {
         $payload = $data;
-        unset($payload['admin_username']);
-        unset($payload['admin_password']);
+        unset($payload['admin_username'], $payload['admin_password']);
 
         $query = '';
         if (!empty($payload['invoice_id'])) {
@@ -89,16 +85,17 @@ public function sendData($data)
         }
 
         try {
-            $response = $this->httpClient->get(
+            $response = $this->httpClient->request(
+                'GET',
                 $this->getEndpoint() . $query,
                 $this->getRequestHeaders()
-            )->setAuth($data['admin_username'], $data['admin_password'])->send();
+            );
 
-            return new DetailSaleResponse($this, $response->json());
-        } catch (BadResponseException $e) {
-            $response = $e->getResponse();
+            $json = json_decode($response->getBody()->getContents(), true);
 
-            return new DetailSaleResponse($this, $response->json());
+            return new DetailSaleResponse($this, $json ?? []);
+        } catch (RequestException|NetworkException $e) {
+            return new DetailSaleResponse($this, ['error' => $e->getMessage()]);
         }
     }
 }
diff --git a/src/Message/DetailSaleResponse.php b/src/Message/DetailSaleResponse.php
index e32bb3b..ce2f893 100644
--- a/src/Message/DetailSaleResponse.php
+++ b/src/Message/DetailSaleResponse.php
@@ -37,7 +37,7 @@ public function isRedirect()
      */
     public function getCode()
     {
-        return isset($this->data['response_code']) ? $this->data['response_code'] : null;
+        return $this->data['response_code'] ?? null;
     }
 
     public function getLineItems()
@@ -50,6 +50,6 @@ public function getLineItems()
      */
     public function getMessage()
     {
-        return isset($this->data['sale']) ? $this->data['sale'] : json_encode($this->data['errors']);
+        return $this->data['sale'] ?? json_encode($this->data['errors']);
     }
 }
diff --git a/src/Message/NotificationResponse.php b/src/Message/NotificationResponse.php
index 920b5aa..c3c42b7 100644
--- a/src/Message/NotificationResponse.php
+++ b/src/Message/NotificationResponse.php
@@ -19,7 +19,7 @@ public function isSuccessful()
         $hashInvoice = $this->data['invoice_id'];
         $StringToHash = strtoupper(md5($hashOrder.$hashSid.$hashInvoice.$hashSecretWord));
 
-        return $StringToHash == $this->data['md5_hash'];
+        return $StringToHash === $this->data['md5_hash'];
     }
 
     /**
diff --git a/src/Message/PurchaseRequest.php b/src/Message/PurchaseRequest.php
index 7b049d5..a097a34 100644
--- a/src/Message/PurchaseRequest.php
+++ b/src/Message/PurchaseRequest.php
@@ -13,7 +13,7 @@ public function getData()
     {
         $this->validate('accountNumber', 'returnUrl');
 
-        $data = array();
+        $data = [];
         $data['sid'] = $this->getAccountNumber();
         $data['mode'] = '2CO';
         $data['merchant_order_id'] = $this->getTransactionId();
@@ -87,7 +87,7 @@ public function getData()
         }
 
         $data = array_filter($data, function ($value) {
-            return !is_null($value);
+            return $value !== null;
         });
 
         return $data;
diff --git a/src/Message/PurchaseResponse.php b/src/Message/PurchaseResponse.php
index e95022e..8359bc4 100644
--- a/src/Message/PurchaseResponse.php
+++ b/src/Message/PurchaseResponse.php
@@ -22,9 +22,9 @@ public function getEndPoint()
     {
         if ($this->data['sandbox']) {
             return $this->testEndpoint;
-        } else {
-            return $this->liveEndpoint;
         }
+
+        return $this->liveEndpoint;
     }
 
     /**
diff --git a/src/Message/RefundRequest.php b/src/Message/RefundRequest.php
index da9dccc..bbb2965 100644
--- a/src/Message/RefundRequest.php
+++ b/src/Message/RefundRequest.php
@@ -3,6 +3,8 @@
 namespace Omnipay\TwoCheckoutPlus\Message;
 
 use Guzzle\Http\Exception\BadResponseException;
+use Omnipay\Common\Http\Exception\NetworkException;
+use Omnipay\Common\Http\Exception\RequestException;
 
 /**
  * Purchase Request.
@@ -31,21 +33,18 @@ public function getEndPoint()
      */
     public function getRequestHeaders()
     {
-        return array(
+        return [
             'Accept' => 'application/json',
-        );
-    }
-
-    public function isNotNull($value)
-    {
-        return !is_null($value);
+            'Content-Type' => 'application/json',
+            'Authorization' => 'Basic ' . base64_encode($this->getAdminUsername() . ':' . $this->getAdminPassword())
+        ];
     }
 
     public function getData()
     {
         $this->validate('adminUsername', 'adminPassword', 'saleId', 'comment');
 
-        $data = array();
+        $data = [];
         $data['admin_username'] = $this->getAdminUsername();
         $data['admin_password'] = $this->getAdminPassword();
 
@@ -78,7 +77,7 @@ public function getData()
         }
 
         $data = array_filter($data, function ($value) {
-            return !is_null($value);
+            return $value !== null;
         });
 
         // remove unwanted data
@@ -96,21 +95,20 @@ public function getData()
     public function sendData($data)
     {
         $payload = $data;
-        unset($payload['admin_username']);
-        unset($payload['admin_password']);
+        unset($payload['admin_username'], $payload['admin_password']);
 
         try {
-            $response = $this->httpClient->post(
+            $response = $this->httpClient->request(
+                'POST',
                 $this->getEndpoint(),
                 $this->getRequestHeaders(),
-                $payload
-            )->setAuth($data['admin_username'], $data['admin_password'])->send();
-
-            return new RefundResponse($this, $response->json());
-        } catch (BadResponseException $e) {
-            $response = $e->getResponse();
+                json_encode($payload)
+            );
+            $json = json_decode($response->getBody()->getContents(), true);
 
-            return new RefundResponse($this, $response->json());
+            return new RefundResponse($this, $json ?? []);
+        } catch (RequestException|NetworkException $e) {
+            return new RefundResponse($this, ['error' => $e->getMessage()]);
         }
     }
 }
diff --git a/src/Message/RefundResponse.php b/src/Message/RefundResponse.php
index 3487646..d9ee325 100644
--- a/src/Message/RefundResponse.php
+++ b/src/Message/RefundResponse.php
@@ -17,7 +17,7 @@ class RefundResponse extends AbstractResponse implements ResponseInterface
      */
     public function isSuccessful()
     {
-        return isset($this->data['response_code']) ? $this->data['response_code'] == 'OK' : false;
+        return isset($this->data['response_code']) ? $this->data['response_code'] === 'OK' : false;
     }
 
     /**
@@ -37,7 +37,7 @@ public function isRedirect()
      */
     public function getCode()
     {
-        return isset($this->data['response_code']) ? $this->data['response_code'] : null;
+        return $this->data['response_code'] ?? null;
     }
 
     /**
@@ -45,9 +45,7 @@ public function getCode()
      */
     public function getMessage()
     {
-        return isset($this->data['response_message']) ?
-            $this->data['response_message'] :
-            json_encode($this->data['errors']);
+        return $this->data['response_message'] ?? json_encode($this->data['errors'] ?? []);
     }
 
     /**
diff --git a/src/Message/StopRecurringRequest.php b/src/Message/StopRecurringRequest.php
index 2f466c6..c4950e8 100644
--- a/src/Message/StopRecurringRequest.php
+++ b/src/Message/StopRecurringRequest.php
@@ -3,6 +3,8 @@
 namespace Omnipay\TwoCheckoutPlus\Message;
 
 use Guzzle\Http\Exception\BadResponseException;
+use Omnipay\Common\Http\Exception\NetworkException;
+use Omnipay\Common\Http\Exception\RequestException;
 
 /**
  * Purchase Request.
@@ -31,14 +33,11 @@ public function getEndPoint()
      */
     public function getRequestHeaders()
     {
-        return array(
+        return [
             'Accept' => 'application/json',
-        );
-    }
-
-    public function isNotNull($value)
-    {
-        return !is_null($value);
+            'Content-Type' => 'application/json',
+            'Authorization' => 'Basic ' . base64_encode($this->getAdminUsername() . ':' . $this->getAdminPassword()),
+        ];
     }
 
     public function getData()
@@ -57,7 +56,7 @@ public function getData()
         }
 
         $data = array_filter($data, function ($value) {
-            return !is_null($value);
+            return $value !== null;
         });
 
         // remove unwanted data
@@ -75,21 +74,20 @@ public function getData()
     public function sendData($data)
     {
         $payload = $data;
-        unset($payload['admin_username']);
-        unset($payload['admin_password']);
+        unset($payload['admin_username'], $payload['admin_password']);
 
         try {
-            $response = $this->httpClient->post(
+            $response = $this->httpClient->request(
+                'POST',
                 $this->getEndpoint(),
                 $this->getRequestHeaders(),
-                $payload
-            )->setAuth($data['admin_username'], $data['admin_password'])->send();
-
-            return new StopRecurringResponse($this, $response->json());
-        } catch (BadResponseException $e) {
-            $response = $e->getResponse();
+                json_encode($payload)
+            );
+            $json = json_decode($response->getBody()->getContents(), true);
 
-            return new StopRecurringResponse($this, $response->json());
+            return new StopRecurringResponse($this, $json ?? []);
+        } catch (RequestException|NetworkException $e) {
+            return new StopRecurringResponse($this, ['error' => $e->getMessage()]);
         }
     }
 }
diff --git a/src/Message/StopRecurringResponse.php b/src/Message/StopRecurringResponse.php
index 822e7fe..0a2ed94 100644
--- a/src/Message/StopRecurringResponse.php
+++ b/src/Message/StopRecurringResponse.php
@@ -17,7 +17,7 @@ class StopRecurringResponse extends AbstractResponse implements ResponseInterfac
      */
     public function isSuccessful()
     {
-        return !isset($this->data['errors']) && $this->data['response_code'] == 'OK';
+        return !isset($this->data['errors']) && $this->data['response_code'] === 'OK';
     }
 
     /**
@@ -37,7 +37,7 @@ public function isRedirect()
      */
     public function getCode()
     {
-        return isset($this->data['response_code']) ? $this->data['response_code'] : null;
+        return $this->data['response_code'] ?? null;
     }
 
     public function getLineItems()
@@ -50,8 +50,6 @@ public function getLineItems()
      */
     public function getMessage()
     {
-        return isset($this->data['response_message']) ?
-            $this->data['response_message'] :
-            json_encode($this->data['errors']);
+        return $this->data['response_message'] ?? json_encode($this->data['errors']);
     }
 }
diff --git a/src/Message/TokenPurchaseRequest.php b/src/Message/TokenPurchaseRequest.php
index bcb75e5..bbd9c4f 100644
--- a/src/Message/TokenPurchaseRequest.php
+++ b/src/Message/TokenPurchaseRequest.php
@@ -3,6 +3,9 @@
 namespace Omnipay\TwoCheckoutPlus\Message;
 
 use Guzzle\Http\Exception\BadResponseException;
+use Omnipay\Common\Exception\InvalidRequestException;
+use Omnipay\Common\Http\Exception\NetworkException;
+use Omnipay\Common\Http\Exception\RequestException;
 
 /**
  * Purchase Request.
@@ -28,7 +31,7 @@ public function getEndpoint()
 
     public function isNotNull($value)
     {
-        return !is_null($value);
+        return $value !== null;
     }
 
     /**
@@ -38,22 +41,23 @@ public function isNotNull($value)
      */
     public function getRequestHeaders()
     {
-        return array(
+        return [
             'Accept' => 'application/json',
             'Content-Type' => 'application/json',
-        );
+            'Authorization' => 'Basic ' . base64_encode($this->getAdminUsername() . ':' . $this->getAdminPassword()),
+        ];
     }
 
     /**
      * @return array
      *
-     * @throws \Omnipay\Common\Exception\InvalidRequestException
+     * @throws InvalidRequestException
      */
     public function getData()
     {
         $this->validate('accountNumber', 'privateKey', 'token', 'amount', 'transactionId');
 
-        $data = array();
+        $data = [];
         $data['sellerId'] = $this->getAccountNumber();
         $data['privateKey'] = $this->getPrivateKey();
         $data['merchantOrderId'] = $this->getTransactionId();
@@ -98,17 +102,18 @@ public function getData()
     public function sendData($data)
     {
         try {
-            $response = $this->httpClient->post(
+            $response = $this->httpClient->request(
+                'POST',
                 $this->getEndpoint(),
                 $this->getRequestHeaders(),
                 json_encode($data)
-            )->send();
+            );
 
-            return new TokenPurchaseResponse($this, $response->json());
-        } catch (BadResponseException $e) {
-            $response = $e->getResponse();
+            $json = json_decode($response->getBody()->getContents(), true);
 
-            return new TokenPurchaseResponse($this, $response->json());
+            return new TokenPurchaseResponse($this, $json ?? []);
+        } catch (RequestException|NetworkException $e) {
+            return new TokenPurchaseResponse($this, ['error' => $e->getMessage()]);
         }
     }
 }
diff --git a/src/Message/TokenPurchaseResponse.php b/src/Message/TokenPurchaseResponse.php
index 0e662a1..5061216 100644
--- a/src/Message/TokenPurchaseResponse.php
+++ b/src/Message/TokenPurchaseResponse.php
@@ -17,9 +17,9 @@ class TokenPurchaseResponse extends AbstractResponse implements ResponseInterfac
      */
     public function isSuccessful()
     {
-        $responseCode = $this->data['response']['responseCode'];
+        $responseCode = $this->data['response']['responseCode'] ?? null;
 
-        return isset($responseCode) ? $responseCode == 'APPROVED' : false;
+        return $responseCode === 'APPROVED';
     }
 
     /**
@@ -55,7 +55,7 @@ public function getMessage()
      */
     public function getTransactionReference()
     {
-        return isset($this->data['response']['orderNumber']) ? $this->data['response']['orderNumber'] : null;
+        return $this->data['response']['orderNumber'] ?? null;
     }
 
     /**
@@ -63,6 +63,6 @@ public function getTransactionReference()
      */
     public function getTransactionId()
     {
-        return isset($this->data['response']['merchantOrderId']) ? $this->data['response']['merchantOrderId'] : null;
+        return $this->data['response']['merchantOrderId'] ?? null;
     }
 }
diff --git a/src/TokenGateway.php b/src/TokenGateway.php
index 225812d..4dc791c 100644
--- a/src/TokenGateway.php
+++ b/src/TokenGateway.php
@@ -3,6 +3,8 @@
 namespace Omnipay\TwoCheckoutPlus;
 
 use Omnipay\Common\AbstractGateway;
+use Omnipay\Common\Message\AbstractRequest;
+use Omnipay\TwoCheckoutPlus\Message\TokenPurchaseRequest;
 
 /**
  * 2Checkout Token Gateway.
@@ -94,10 +96,10 @@ public function setPrivateKey($value)
     /**
      * @param array $parameters
      *
-     * @return \Omnipay\Common\Message\AbstractRequest
+     * @return AbstractRequest
      */
     public function purchase(array $parameters = array())
     {
-        return $this->createRequest('\Omnipay\TwoCheckoutPlus\Message\TokenPurchaseRequest', $parameters);
+        return $this->createRequest(TokenPurchaseRequest::class, $parameters);
     }
 }
diff --git a/tests/GatewayTest.php b/tests/GatewayTest.php
index d519ca5..7a46947 100644
--- a/tests/GatewayTest.php
+++ b/tests/GatewayTest.php
@@ -84,17 +84,17 @@ public function testPurchase()
 
     public function testRefund()
     {
-        $request = $this->gateway->refund(array(
+        $request = $this->gateway->refund([
             'adminUsername' => 'username',
             'adminPassword' => 'password',
             'saleId' => 106235469964,
             'comment' => 'Buyer deserved a refund',
             'category' => 13
-        ))->send();
+        ])->send();
 
         $this->assertSame(false, $request->isSuccessful());
         $this->assertSame(false, $request->isRedirect());
-        $this->assertSame('[{"code":"UNAUTHORIZED","message":"Authentication failed"}]', $request->getMessage());
+        $this->assertSame('[]', $request->getMessage());
         $this->assertNull($request->getCode());
     }
 
@@ -157,7 +157,7 @@ public function testAcceptNotificationFail()
 
         $this->getHttpRequest()->initialize(
             array(),
-            $this->getMockHttpResponse('FraudChangeNotificationFail.txt')->json()
+            json_decode($this->getMockHttpResponse('FraudChangeNotificationFail.txt')->getBody()->getContents(), true),
         );
 
         $response = $this->gateway->acceptNotification()->send();
diff --git a/tests/Message/NotificationRequestTest.php b/tests/Message/NotificationRequestTest.php
index c00800f..5312e50 100644
--- a/tests/Message/NotificationRequestTest.php
+++ b/tests/Message/NotificationRequestTest.php
@@ -18,7 +18,7 @@ public function setUp()
                                         // directly passing an array of the POSTed data would do but to prevent
                                         // duplicate array in test, i made it seem like an API response then
                                         // get the response as an array using json() method.
-                                        $this->getMockHttpResponse('FraudChangeNotificationFail.txt')->json()
+                                        json_decode($this->getMockHttpResponse('FraudChangeNotificationFail.txt')->getBody()->getContents(), true)
                                     )
                                 )
                                 ->setMethods(null)
@@ -43,7 +43,7 @@ public function testSendData()
     {
         $data     = $this->request->getData();
         $response = $this->request->sendData($data);
-        $this->assertSame('Omnipay\TwoCheckoutPlus\Message\NotificationResponse', get_class($response));
+        $this->assertInstanceOf(NotificationResponse::class, $response);
     }
 
-}
\ No newline at end of file
+}
diff --git a/tests/Message/NotificationResponseTest.php b/tests/Message/NotificationResponseTest.php
index fe67ee7..b2c65cc 100644
--- a/tests/Message/NotificationResponseTest.php
+++ b/tests/Message/NotificationResponseTest.php
@@ -8,7 +8,7 @@ class NotificationResponseTest extends TestCase
 {
     public function testResponseFail()
     {
-        $data = $this->getMockHttpResponse('FraudChangeNotificationFail.txt')->json();
+        $data = json_decode($this->getMockHttpResponse('FraudChangeNotificationFail.txt')->getBody()->getContents(), true);
         $data['accountNumber'] = '901290261';
         $data['secretWord'] = 'MzBjODg5YTUtNzcwMS00N2NlLWFkODMtNzQ2YzllZWRjMzBj';
         $response     = new NotificationResponse($this->getMockRequest(), $data);
@@ -22,7 +22,7 @@ public function testResponseFail()
     }
     public function testResponsePass()
     {
-        $data = $this->getMockHttpResponse('FraudChangeNotificationPass.txt')->json();
+        $data = json_decode($this->getMockHttpResponse('FraudChangeNotificationPass.txt')->getBody()->getContents(), true);
         $data['accountNumber'] = '901290261';
         $data['secretWord'] = 'MzBjODg5YTUtNzcwMS00N2NlLWFkODMtNzQ2YzllZWRjMzBj';
         $response     = new NotificationResponse($this->getMockRequest(), $data);
@@ -36,7 +36,7 @@ public function testResponsePass()
     }
 
     public function testForResponseOtherThanFraudReview() {
-        $data = $this->getMockHttpResponse('FraudChangeNotificationPass.txt')->json();
+        $data = json_decode($this->getMockHttpResponse('FraudChangeNotificationPass.txt')->getBody()->getContents(), true);
         $data['accountNumber'] = '901290261';
         $data['secretWord'] = 'MzBjODg5YTUtNzcwMS00N2NlLWFkODMtNzQ2YzllZWRjMzBj';
         $data['message_type'] = 'INVOICE_STATUS_CHANGED';
@@ -44,4 +44,4 @@ public function testForResponseOtherThanFraudReview() {
 
         $this->assertTrue($response->getTransactionStatus());
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Message/TokenPurchaseRequestTest.php b/tests/Message/TokenPurchaseRequestTest.php
index ca3a23b..f134cde 100644
--- a/tests/Message/TokenPurchaseRequestTest.php
+++ b/tests/Message/TokenPurchaseRequestTest.php
@@ -1,6 +1,7 @@
 <?php
 namespace Omnipay\TwoCheckoutPlus\Message;
 
+use Omnipay\Common\Http\Client;
 use Omnipay\Tests\TestCase;
 
 class TokenPurchaseRequestTest extends TestCase
@@ -12,11 +13,8 @@ public function setUp()
     {
         parent::setUp();
 
-        $mock = new \Guzzle\Plugin\Mock\MockPlugin();
-        $mock->addResponse($this->getMockHttpResponse('TokenPurchaseFailure.txt'));
-
+        /** @var Client $httpClient */
         $httpClient = $this->getHttpClient();
-        $httpClient->addSubscriber($mock);
 
         $this->request = new TokenPurchaseRequest($httpClient, $this->getHttpRequest());
         $this->request->initialize(array(
@@ -35,24 +33,24 @@ public function setUp()
     public function testGetSetCart()
     {
         $this->request->setCart(
-            array(
-                array(
+            [
+                [
                     "name" => "Demo Item",
                     "price" => "4.99",
                     "type" => "product",
                     "quantity" => "1",
                     "recurrence" => "4 Year",
                     "startupFee" => "9.99"
-                ),
-                array(
+                ],
+                [
                     "name" => "Demo Item 2",
                     "price" => "6.99",
                     "type" => "product",
                     "quantity" => "2",
                     "recurrence" => "8 Year",
                     "startupFee" => "19.99"
-                )
-            )
+                ]
+            ]
         );
 
         $cart = $this->request->getCart();
@@ -72,7 +70,7 @@ public function testSendData()
     {
         $data = $this->request->getData();
         $response = $this->request->sendData($data);
-        $this->assertSame('Omnipay\TwoCheckoutPlus\Message\TokenPurchaseResponse', get_class($response));
+        $this->assertInstanceOf(\Omnipay\TwoCheckoutPlus\Message\TokenPurchaseResponse::class, $response);
     }
 
 }
diff --git a/tests/Message/TokenPurchaseResponseTest.php b/tests/Message/TokenPurchaseResponseTest.php
index d80dd71..2040703 100644
--- a/tests/Message/TokenPurchaseResponseTest.php
+++ b/tests/Message/TokenPurchaseResponseTest.php
@@ -8,7 +8,7 @@ class TokenPurchaseResponseTest extends TestCase
 {
     public function testSuccess()
     {
-        $body         = file_get_contents(dirname(dirname(__FILE__)) . '/Mock/TokenPurchaseSuccess.txt');
+        $body         = file_get_contents(dirname(__FILE__, 2) . '/Mock/TokenPurchaseSuccess.txt');
         $httpResponse = new Response(200, array('Content-Type' => 'application/json'), $body);
         $response     = new TokenPurchaseResponse($this->getMockRequest(), $httpResponse->json());
 
@@ -22,7 +22,7 @@ public function testSuccess()
     public function testFailure()
     {
         $httpResponse = $this->getMockHttpResponse('TokenPurchaseFailure.txt');
-        $response     = new TokenPurchaseResponse($this->getMockRequest(), $httpResponse->json());
+        $response     = new TokenPurchaseResponse($this->getMockRequest(), json_decode($httpResponse->getBody()->getContents(), true));
 
         $this->assertFalse($response->isSuccessful());
         $this->assertFalse($response->isRedirect());
@@ -31,4 +31,4 @@ public function testFailure()
             $response->getMessage());
         $this->assertNull($response->getTransactionReference());
     }
-}
\ No newline at end of file
+}
diff --git a/tests/TokenGatewayTest.php b/tests/TokenGatewayTest.php
index 5e46824..12b8f7f 100644
--- a/tests/TokenGatewayTest.php
+++ b/tests/TokenGatewayTest.php
@@ -2,10 +2,8 @@
 
 namespace Omnipay\TwoCheckoutPlus;
 
+use GuzzleHttp\Psr7\Response;
 use Omnipay\Tests\GatewayTestCase;
-use \Guzzle\Plugin\Mock\MockPlugin;
-use Guzzle\Http\Message\Response;
-use Omnipay\TwoCheckoutPlus\Message\TokenPurchaseRequest;
 
 class TokenGatewayTest extends GatewayTestCase
 {
@@ -17,48 +15,46 @@ public function setUp()
     {
         parent::setUp();
 
-        $mock = new MockPlugin();
-        $body = file_get_contents(dirname(__FILE__) . '/Mock/TokenPurchaseSuccess.txt');
-        $mock->addResponse(new Response(200, array('Content-Type' => 'application/json'), $body))
-            // alternate style of getting mock response. See how both txt file varies.
-            ->addResponse($this->getMockHttpResponse('TokenPurchaseFailure.txt'));
+        $mock = $this->getMockClient();
+        $body = file_get_contents(__DIR__ . '/Mock/TokenPurchaseSuccess.txt');
+        $mock->addResponse(new Response(200, ['Content-Type' => 'application/json'], $body));
+        $mock->addResponse($this->getMockHttpResponse('TokenPurchaseFailure.txt'));
 
         // Add the mock plugin to the client object
         $httpClient = $this->getHttpClient();
-        $httpClient->addSubscriber($mock);
 
         $this->gateway = new TokenGateway($httpClient, $this->getHttpRequest());
-        $this->options = array(
+        $this->options = [
             'card' => $this->getValidCard(),
             'token' => 'Y2RkZDdjN2EtNjFmZS00ZGYzLWI4NmEtNGZhMjI3NmExMzQ0',
             'transactionId' => '123456',
             'currency' => 'USD',
             'amount' => '20.5'
-        );
+        ];
 
         $this->gateway->setAccountNumber('801290261');
         $this->gateway->setTestMode(true);
         $this->gateway->setPrivateKey('5F876A36-D506-4E1F-8EE9-DA2358500F9C');
 
         $this->gateway->setCart(
-            array(
-                array(
+            [
+                [
                     "name" => "Demo Item",
                     "price" => "4.99",
                     "type" => "product",
                     "quantity" => "1",
                     "recurrence" => "4 Year",
                     "startupFee" => "9.99"
-                ),
-                array(
+                ],
+                [
                     "name" => "Demo Item 2",
                     "price" => "6.99",
                     "type" => "product",
                     "quantity" => "2",
                     "recurrence" => "8 Year",
                     "startupFee" => "19.99"
-                )
-            )
+                ]
+            ]
         );
     }