Add account top-up functionality

Resolves #53

Author: mheap

src/Account/Client.php

@@ -73,4 +73,42 @@ public function getBalance()
         $balance = new Balance($body['value'], $body['autoReload']);
         return $balance;
     }
+
+    public function topUp($trx)
+    {
+        $body = [
+            'trx' => $trx
+        ];
+
+        $request = new Request(
+            \Nexmo\Client::BASE_REST . '/account/top-up'
+            ,'POST'
+            , 'php://temp'
+            , ['content-type' => 'application/x-www-form-urlencoded']
+        );
+
+        $request->getBody()->write(http_build_query($body));
+        $response = $this->client->send($request);
+
+        if($response->getStatusCode() != '200'){
+            throw $this->getException($response, $application);
+        }
+    }
+
+    protected function getException(ResponseInterface $response, $application = null)
+    {
+        $body = json_decode($response->getBody()->getContents(), true);
+        $status = $response->getStatusCode();
+
+        if($status >= 400 AND $status < 500) {
+            $e = new Exception\Request($body['error_title'], $status);
+        } elseif($status >= 500 AND $status < 600) {
+            $e = new Exception\Server($body['error_title'], $status);
+        } else {
+            $e = new Exception\Exception('Unexpected HTTP Status Code');
+        }
+
+        return $e;
+    }
+
 }

test/Account/ClientTest.php

@@ -35,10 +35,20 @@ public function setUp()
         $this->nexmoClient = $this->prophesize('Nexmo\Client');
         $this->accountClient = new Client();
         $this->accountClient->setClient($this->nexmoClient->reveal());
+    }
+
+    public function testTopUp()
+    {
+        $this->nexmoClient->send(Argument::that(function (RequestInterface $request) {
+            $this->assertEquals('/account/top-up', $request->getUri()->getPath());
+            $this->assertEquals('rest.nexmo.com', $request->getUri()->getHost());
+            $this->assertEquals('POST', $request->getMethod());
+            $this->assertRequestFormBodyContains('trx', 'ABC123', $request);
+
+            return true;
+        }))->shouldBeCalledTimes(1)->willReturn($this->getResponse('empty'));
 
-        $basic  = new \Nexmo\Client\Credentials\Basic('7c9738e6','5e840647a5b710a011A');
-        $client = new \Nexmo\Client($basic);
-        //$this->accountClient->setClient($client);
+        $this->accountClient->topUp('ABC123');
     }
 
     public function testGetBalance()