@Test
public void testCustomKeyValue() throws ClassNotFoundException,
    InstantiationException, IllegalAccessException {

  Interceptor.Builder builder = InterceptorBuilderFactory.newInstance(
      InterceptorType.STATIC.toString());
  Context ctx = new Context();
  ctx.put(Constants.KEY, "myKey");
  ctx.put(Constants.VALUE, "myVal");
  builder.configure(ctx);
  Interceptor interceptor = builder.build();
  Event event = EventBuilder.withBody("test", Charsets.UTF_8);
  Assert.assertNull(event.getHeaders().get("myKey"));
  event = interceptor.intercept(event);
  String val = event.getHeaders().get("myKey");
  Assert.assertNotNull(val);
  Assert.assertEquals("myVal", val);
}