### Question:
IF_UNUSED extends ISOFieldPackager { public byte[] pack (ISOComponent c) throws ISOException { throw new ISOException("IF_UNUSED: Packager should not pack field " + c.getKey()); } IF_UNUSED(); byte[] pack(ISOComponent c); int unpack(ISOComponent c, byte[] b, int offset); int getMaxPackedLength();  }### Answer:
@Test public void testPack() throws Exception { ISOField field = new ISOField(12, "ABCD"); IF_UNUSED packager = new IF_UNUSED(); try { packager.pack(field); fail("Should have thrown an exception"); } catch (Exception expected) { } }