#30: Extend isErrorAlreadyAdded check to also check column name so se…

…veral columns in the same row may throw the same error and they can be distinguished.

app/code/Magento/ImportExport/Model/Import/ErrorProcessing/ProcessingErrorAggregator.php

@@ -77,7 +77,7 @@ public function addError(
         $errorMessage = null,
         $errorDescription = null
     ) {
-        if ($this->isErrorAlreadyAdded($rowNumber, $errorCode)) {
+        if ($this->isErrorAlreadyAdded($rowNumber, $errorCode, $columnName)) {
             return $this;
         }
         $this->processErrorStatistics($errorLevel);
@@ -333,13 +333,14 @@ public function clear()
     /**
      * @param int $rowNum
      * @param string $errorCode
+     * @param string $columnName
      * @return bool
      */
-    protected function isErrorAlreadyAdded($rowNum, $errorCode)
+    protected function isErrorAlreadyAdded($rowNum, $errorCode, $columnName = null)
     {
         $errors = $this->getErrorsByCode([$errorCode]);
         foreach ($errors as $error) {
-            if ($rowNum == $error->getRowNumber()) {
+            if ($rowNum == $error->getRowNumber() && $columnName == $error->getColumnName()) {
                 return true;
             }
         }