added phpunit test cases

Author: kshitij verma

README.md

@@ -88,7 +88,7 @@ $ composer require shopifychamp/shopify-api-php-sdk
     ```
     if($client->hasNextPage())
     {
-        $next_page_response $client->call('GET','products',['limit'=>20,'page_info'=>$client->getNextPage()]);
+        $next_page_response = $client->call('GET','products',['limit'=>20,'page_info'=>$client->getNextPage()]);
         print_r($next_page_response);
     }
     ```
@@ -98,7 +98,7 @@ $ composer require shopifychamp/shopify-api-php-sdk
     ```
     if($client->hasPrevPage())
     {
-        $prev_page_response $client->call('GET','products',['limit'=>20,'page_info'=>$client->getPrevPage()]);
+        $prev_page_response = $client->call('GET','products',['limit'=>20,'page_info'=>$client->getPrevPage()]);
         print_r($prev_page_response);
     }
     ```

test/privateapp.php

@@ -12,7 +12,14 @@
     $client = new Shopify\PrivateApp($shop, $api_key, $password, $api_params);
     /**rest api call**/
     $response = $client->call('GET', 'products', ['limit' => 1]);
-    print_r($response);
+    if($client->hasNextPage()){
+        $response = $client->call('GET','products',[
+            'limit'=>20,
+            'page_info'=>$client->getNextPage()
+        ]);
+        print_r($response);
+    }
+
 }
 catch (\Shopify\Exception\ApiException $e)
 {

test/publicapp.php

@@ -17,8 +17,16 @@
     {
         if($access_token = $client->getAccessToken($_GET)){
             $client->setAccessToken($access_token);
-            print_r($access_token);
+            $response = $client->call('GET', 'products', ['limit' => 1]);
+            if($client->hasNextPage()){
+                $response = $client->call('GET','products',[
+                    'limit'=>20,
+                    'page_info'=>$client->getNextPage()
+                ]);
+                print_r($response);
+            }
         }
+
     }else{
         $redirect_url= isset($_SERVER["HTTPS"]) && $_SERVER["HTTPS"] == "on"?'https://':'http://';
         if ($_SERVER["SERVER_PORT"] != "80") {
@@ -29,8 +37,6 @@
 
         header('Location: '.urldecode($client->prepareAuthorizeUrl($redirect_url)));
     }
-
-
 }catch (\Shopify\Exception\ApiException $e){
     echo "Errors: ".$e->getError().'<br> status code: '.$e->getCode();
 }