### Question:
IncomingInvoiceExport { public static String deriveCodaElement1FromBuyer(Party buyer) { if (buyer==null) return null; if (buyer.getReference().equals("BE00")){ return "BE01EUR"; } return buyer.getReference().concat("EUR"); } 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 deriveCodaElement1FromBuyer() throws Exception { Party buyer = new Organisation(); Assertions.assertThat(IncomingInvoiceExport.deriveCodaElement1FromBuyer(null)).isNull(); buyer.setReference("SOMETHING"); Assertions.assertThat(IncomingInvoiceExport.deriveCodaElement1FromBuyer(buyer)).isEqualTo("SOMETHINGEUR"); buyer.setReference("BE00"); Assertions.assertThat(IncomingInvoiceExport.deriveCodaElement1FromBuyer(buyer)).isEqualTo("BE01EUR"); }