public function testGetInvoiceReturnsCorrectData()
 {
     $this->setMockResponse($this->client, array('invoices/getInvoice'));
     $invoice = $this->client->getInvoice(1);
     $this->assertInstanceOf('\\Mgrt\\Model\\Invoice', $invoice);
     $invoiceLines = $invoice->getInvoiceLines();
     foreach ($invoiceLines as $invoiceLine) {
         $this->assertInstanceOf('\\Mgrt\\Model\\InvoiceLine', $invoiceLine);
     }
 }