MC-42612: Negative discount amount displays on order page in admin for product $0.00 price

- Do not apply rounding delta on the discount amount when the product price is 0

Author: loganadhan-palanisamy

app/code/Magento/SalesRule/Model/Utility.php

@@ -195,7 +195,8 @@ public function deltaRoundingFix(
         //TODO Seems \Magento\Quote\Model\Quote\Item\AbstractItem::getDiscountPercent() returns float value
         //that can not be used as array index
         $percentKey = $item->getDiscountPercent();
-        if ($percentKey) {
+        $rowTotal = $item->getRowTotal();
+        if ($percentKey && $rowTotal > 0) {
             $delta = isset($this->_roundingDeltas[$percentKey]) ? $this->_roundingDeltas[$percentKey] : 0;
             $baseDelta = isset($this->_baseRoundingDeltas[$percentKey]) ? $this->_baseRoundingDeltas[$percentKey] : 0;
 

app/code/Magento/SalesRule/Test/Unit/Model/UtilityTest.php

@@ -463,6 +463,7 @@ public function testDeltaRoundignFix()
         $discountAmount = 10.003;
         $baseDiscountAmount = 12.465;
         $percent = 15;
+        $rowTotal = 100;
         $roundedDiscount = round($discountAmount, 2);
         $roundedBaseDiscount = round($baseDiscountAmount, 2);
         $delta = $discountAmount - $roundedDiscount;
@@ -491,6 +492,7 @@ public function testDeltaRoundignFix()
             ->willReturn($store);
 
         $this->item->setDiscountPercent($percent);
+        $this->item->setRowTotal($rowTotal);
 
         $discountData = $this->createMock(Data::class);
         $discountData->expects($this->at(0))
@@ -523,7 +525,6 @@ public function testDeltaRoundignFix()
 
         $this->assertEquals($this->utility, $this->utility->deltaRoundingFix($discountData, $this->item));
         $this->assertEquals($this->utility, $this->utility->deltaRoundingFix($discountData, $this->item));
-
     }
 
     public function testResetRoundingDeltas()