/** The HTTP {@code Content-Type} header field name. */
  public static final String CONTENT_TYPE = "Content-Type";
  /** The HTTP {@code Date} header field name. */
  public static final String DATE = "Date";
  /** The HTTP {@code Pragma} header field name. */
  public static final String PRAGMA = "Pragma";
  /** The HTTP {@code Via} header field name. */
  public static final String VIA = "Via";

         * the new one. The result is a ConcurrentModificationException or other bad behavior.
         *
         * (If we decide that we really, really hate allocating two Iterators per cycle instead of
         * one, we can optimistically store the new Iterator and then be willing to throw it out if
         * the user calls remove().)
         */

    Builder<String, Integer> builder =
        new Builder<String, Integer>()
            .put("one", 1)
            .put("one", 1); // throwing on this line might be better but it's too late to change

    try {
      builder.buildOrThrow();
      fail();
    } catch (IllegalArgumentException expected) {
    }
  }

  public void testBuildKeepingLast_allowsOverwrite() {