### Question:
IncomingInvoiceExport { public static String getCodaElement6FromSellerReference(final String sellerReference){ if (sellerReference.startsWith("FR")) { return "FRFO".concat(sellerReference.substring(2)); } if (sellerReference.startsWith("BE")){ return "BEFO".concat(sellerReference.substring(2)); } return null; } IncomingInvoiceExport(
            final IncomingInvoiceItem item,
            final String documentNumber,
            final String comments
    ); static String deriveCodaElement1FromBuyer(Party buyer); static String getCodaElement6FromSellerReference(final String sellerReference); static String deriveCodaElement3FromPropertyAndIncomingInvoiceType(final FixedAsset property, final IncomingInvoiceType incomingInvoiceType, final String atPath);  }### Answer:
@Test public void getCodaElement6FromSellerReference() { String frenchSupplierRef = "FR12345"; Assertions.assertThat(IncomingInvoiceExport.getCodaElement6FromSellerReference(frenchSupplierRef)).isEqualTo("FRFO12345"); String belgianSupplierRef = "BE123456"; Assertions.assertThat(IncomingInvoiceExport.getCodaElement6FromSellerReference(belgianSupplierRef)).isEqualTo("BEFO123456"); String unknownSupplierRef = "UN123456"; Assertions.assertThat(IncomingInvoiceExport.getCodaElement6FromSellerReference(unknownSupplierRef)).isNull(); }