diff --git a/library/src/test/java/org/mustangproject/ZUGFeRD/ItemSellerTradePartyTest.java b/library/src/test/java/org/mustangproject/ZUGFeRD/ItemSellerTradePartyTest.java
new file mode 100644
index 00000000..12af7493
--- /dev/null
+++ b/library/src/test/java/org/mustangproject/ZUGFeRD/ItemSellerTradePartyTest.java
@@ -0,0 +1,105 @@
+package org.mustangproject.ZUGFeRD;
+
+import org.junit.Test;
+import org.mustangproject.Invoice;
+import org.mustangproject.Item;
+import org.mustangproject.Product;
+import org.mustangproject.TradeParty;
+
+import java.math.BigDecimal;
+import java.nio.charset.StandardCharsets;
+import java.util.Date;
+
+import static org.xmlunit.assertj.XmlAssert.assertThat;
+
+public class ItemSellerTradePartyTest {
+
+    /**
+     * Item de test qui force un ItemSellerTradeParty au niveau ligne
+     * via la nouvelle méthode IZUGFeRDExportableItem#getItemSellerTradeParty().
+     */
+    private static class ItemWithItemSellerTradeParty extends Item {
+        private final TradeParty itemSeller;
+
+        ItemWithItemSellerTradeParty(Product product, BigDecimal price, BigDecimal quantity, TradeParty itemSeller) {
+            super(product, price, quantity);
+            this.itemSeller = itemSeller;
+        }
+
+        @Override
+        public TradeParty getLineSeller() {
+            return itemSeller;
+        }
+    }
+
+    @Test
+    public void testLineLevelItemSellerTradePartyIsExportedOnlyWhenProvided() {
+        // Header seller = vendeur contractuel (collectivité émettrice)
+        TradeParty contractualSeller = new TradeParty("Mairie A", "1 rue A", "75001", "Paris", "FR");
+        // Line-level "actual service provider" (autre collectivité)
+        TradeParty actualServiceProvider = new TradeParty("Mairie B", "2 rue B", "69001", "Lyon", "FR");
+        // Buyer
+        TradeParty buyer = new TradeParty("Client X", "3 rue C", "33000", "Bordeaux", "FR");
+
+        Product service = new Product("Prestation", "Service intercommunal", "C62", new BigDecimal("20.00"));
+
+        // Ligne 1 : avec ItemSellerTradeParty
+        Item line1 = new ItemWithItemSellerTradeParty(
+                service,
+                new BigDecimal("100.00"),
+                new BigDecimal("1"),
+                actualServiceProvider
+        );
+
+        // Ligne 2 : sans ItemSellerTradeParty (null via default getter)
+        Item line2 = new Item(
+                service,
+                new BigDecimal("50.00"),
+                new BigDecimal("1")
+        );
+
+        Invoice inv = new Invoice()
+                .setNumber("INV-ITEM-SELLER-001")
+                .setIssueDate(new Date())
+                .setDeliveryDate(new Date())
+                .setDueDate(new Date())
+                .setSender(contractualSeller)
+                .setRecipient(buyer)
+                .setCurrency("EUR")
+                .addItem(line1)
+                .addItem(line2);
+
+        ZUGFeRD2PullProvider provider = new ZUGFeRD2PullProvider();
+        provider.setProfile(Profiles.getByName("EXTENDED"));
+        provider.generateXML(inv);
+
+        String xml = new String(provider.getXML(), StandardCharsets.UTF_8);
+
+        // 1) Le Seller header doit rester "Mairie A"
+        assertThat(xml)
+                .valueByXPath("//*[local-name()='ApplicableHeaderTradeAgreement']" +
+                        "/*[local-name()='SellerTradeParty']" +
+                        "/*[local-name()='Name']")
+                .isEqualTo("Mairie A");
+
+        // 2) Ligne 1 : ItemSellerTradeParty présent, et correspond à "Mairie B"
+        assertThat(xml)
+                .nodesByXPath("(//*[local-name()='IncludedSupplyChainTradeLineItem'])[1]" +
+                        "//*[local-name()='SpecifiedLineTradeAgreement']" +
+                        "/*[local-name()='ItemSellerTradeParty']")
+                .exist();
+
+        assertThat(xml)
+                .valueByXPath("(//*[local-name()='IncludedSupplyChainTradeLineItem'])[1]" +
+                        "//*[local-name()='ItemSellerTradeParty']" +
+                        "/*[local-name()='Name']")
+                .isEqualTo("Mairie B");
+
+         // 3) Ligne 2 : ItemSellerTradeParty absent
+        assertThat(xml)
+                .nodesByXPath("(//*[local-name()='IncludedSupplyChainTradeLineItem'])[2]" +
+                        "//*[local-name()='SpecifiedLineTradeAgreement']" +
+                        "/*[local-name()='ItemSellerTradeParty']").isEmpty();
+     
+    }
+}