MAGETWO-91769: Credit Memo - Wrong tax calculation! #10982

- Added possibility to recalculate tax amounts in case of '0' shipping value refund

Author: epamt

app/code/Magento/Sales/Model/Order/Creditmemo/Total/Tax.php

@@ -5,9 +5,14 @@
  */
 namespace Magento\Sales\Model\Order\Creditmemo\Total;
 
+/**
+ * Order credit memo tax total calculation model
+ */
 class Tax extends AbstractTotal
 {
     /**
+     * Collect credit memo tax total
+     *
      * @param \Magento\Sales\Model\Order\Creditmemo $creditmemo
      * @return $this
      *
@@ -72,7 +77,7 @@ public function collect(\Magento\Sales\Model\Order\Creditmemo $creditmemo)
         $isPartialShippingRefunded = false;
         if ($invoice = $creditmemo->getInvoice()) {
             //recalculate tax amounts in case if refund shipping value was changed
-            if ($order->getBaseShippingAmount() && $creditmemo->getBaseShippingAmount()) {
+            if ($order->getBaseShippingAmount() && $creditmemo->getBaseShippingAmount() !== null) {
                 $taxFactor = $creditmemo->getBaseShippingAmount() / $order->getBaseShippingAmount();
                 $shippingTaxAmount = $invoice->getShippingTaxAmount() * $taxFactor;
                 $baseShippingTaxAmount = $invoice->getBaseShippingTaxAmount() * $taxFactor;

app/code/Magento/Sales/Test/Unit/Model/Order/Creditmemo/Total/TaxTest.php

@@ -447,10 +447,10 @@ public function collectDataProvider()
                     ],
                 ],
                 'creditmemo_data' => [
-                    'grand_total' => 64.95,
-                    'base_grand_total' => 64.95,
-                    'tax_amount' => 4.95,
-                    'base_tax_amount' => 4.95,
+                    'grand_total' => 64.94,
+                    'base_grand_total' => 64.94,
+                    'tax_amount' => 4.94,
+                    'base_tax_amount' => 4.94,
                 ],
             ],
         ];