Add factory method createCalculator() in ZUGFeRD2PullProvider to allo…

library/src/main/java/org/mustangproject/ZUGFeRD/ZUGFeRD2PullProvider.java

@@ -339,10 +339,14 @@ protected String getItemTotalAllowanceChargeStr(IZUGFeRDAllowanceCharge allowanc
 		return itemTotalAllowanceChargeStr;
 	}
 
+	protected TransactionCalculator createCalculator(IExportableTransaction trans) {
+   		 return new TransactionCalculator(trans);
+	}	
+
 	@Override
 	public void generateXML(IExportableTransaction trans) {
 		this.trans = trans;
-		this.calc = new TransactionCalculator(trans);
+		this.calc = createCalculator(trans);
 
 		boolean hasDueDate = trans.getDueDate() != null;
 		final SimpleDateFormat germanDateFormat = new SimpleDateFormat("dd.MM.yyyy");

library/src/test/java/org/mustangproject/ZUGFeRD/ZUGFeRD2PullProviderFactoryTest.java

@@ -0,0 +1,71 @@
+package org.mustangproject.ZUGFeRD;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.math.BigDecimal;
+import java.util.Date;
+
+import org.junit.jupiter.api.Test;
+import org.mustangproject.Invoice;
+import org.mustangproject.Item;
+import org.mustangproject.Product;
+import org.mustangproject.TradeParty;
+
+public class ZUGFeRD2PullProviderFactoryTest {
+
+	static class TestTransactionCalculator extends TransactionCalculator {
+
+		private boolean called = false;
+
+		public TestTransactionCalculator(IExportableTransaction trans) {
+			super(trans);
+		}
+
+		@Override
+		public BigDecimal getGrandTotal() {
+			called = true;
+			return BigDecimal.valueOf(999.99);
+		}
+
+		public boolean wasCalled() {
+			return called;
+		}
+	}
+
+	static class TestPullProvider extends ZUGFeRD2PullProvider {
+
+		private TestTransactionCalculator calculator;
+
+		@Override
+		protected TransactionCalculator createCalculator(IExportableTransaction trans) {
+			calculator = new TestTransactionCalculator(trans);
+			return calculator;
+		}
+
+		public TestTransactionCalculator getCalculator() {
+			return calculator;
+		}
+	}
+
+	@Test
+	void customCalculatorIsUsed() throws Exception {
+
+		TradeParty buyer = new TradeParty("Client X", "3 rue C", "33000", "Bordeaux", "FR");
+		TradeParty seller = new TradeParty("Mairie A", "1 rue A", "75001", "Paris", "FR");
+
+		Invoice invoice = new Invoice().setNumber("INV-CALC-001").setIssueDate(new Date()).setDeliveryDate(new Date())
+				.setDueDate(new Date()).setCurrency("EUR").setSender(buyer).setRecipient(seller);
+
+		Product service = new Product("Prestation", "Service intercommunal", "C62", new BigDecimal("20.00"));
+
+		invoice.addItem(new Item(service, BigDecimal.ONE, BigDecimal.TEN).setTax(BigDecimal.valueOf(20)));
+
+		TestPullProvider provider = new TestPullProvider();
+
+		provider.generateXML(invoice);
+
+		assertNotNull(provider.getCalculator());
+		assertTrue(provider.getCalculator().wasCalled());
+	}
+}