### Question:
AppendFunction implements Function<String, String> { @Override public String apply(String input) { return new StringBuilder().append(input).append(myString).toString(); } AppendFunction(String string); @Override String apply(String input);  }### Answer:
@Test public void testApply() { Assert.assertEquals("Knock knock Who's there?", new AppendFunction("Who's there?").apply("Knock knock ")); }