MAGETWO-11669: API salesRefundInvoiceV1 does no save invoice ID on credit memo

app/code/Magento/Sales/Model/RefundInvoice.php

@@ -175,6 +175,7 @@ public function execute(
                     $invoice->getBaseTotalRefunded() + $creditmemo->getBaseGrandTotal()
                 );
             }
+            $creditmemo->setInvoiceId($invoice->getId());
             $this->invoiceRepository->save($invoice);
             $order = $this->orderRepository->save($order);
             $creditmemo = $this->creditmemoRepository->save($creditmemo);

app/code/Magento/Sales/Test/Unit/Model/RefundInvoiceTest.php

@@ -100,7 +100,7 @@ class RefundInvoiceTest extends \PHPUnit\Framework\TestCase
     private $orderMock;
 
     /**
-     * @var OrderInterface|\PHPUnit_Framework_MockObject_MockObject
+     * @var InvoiceInterface|\PHPUnit_Framework_MockObject_MockObject
      */
     private $invoiceMock;
 
@@ -186,6 +186,7 @@ protected function setUp()
             ->getMockForAbstractClass();
 
         $this->invoiceMock = $this->getMockBuilder(InvoiceInterface::class)
+            ->setMethods(['getId'])
             ->disableOriginalConstructor()
             ->getMockForAbstractClass();
 
@@ -239,6 +240,9 @@ public function testOrderCreditmemo($invoiceId, $isOnline, $items, $notify, $app
         $this->invoiceRepositoryMock->expects($this->once())
             ->method('get')
             ->willReturn($this->invoiceMock);
+        $this->invoiceMock->expects($this->once())
+            ->method('getId')
+            ->willReturn($invoiceId);
         $this->orderRepositoryMock->expects($this->once())
             ->method('get')
             ->willReturn($this->orderMock);