### Question:
ShoppingCartEntry implements Serializable { public static ShoppingCartEntry instance(final String fileName) { return new ShoppingCartEntry(fileName); } private  ShoppingCartEntry(final String fileName); static ShoppingCartEntry instance(final String fileName); @Override String toString(); String getFileName();  }### Answer:
@Test public void testInstance() throws Exception { String fileName = "huh"; ShoppingCartEntry entry = ShoppingCartEntry.instance(fileName); Assert.assertEquals("did not set file name", fileName, entry.getFileName()); }
@Test(expected = IllegalArgumentException.class) public void testInstanceNullFile() throws Exception { ShoppingCartEntry.instance(null); }
@Test(expected = IllegalArgumentException.class) public void testInstanceBlankFile() throws Exception { ShoppingCartEntry.instance(""); }