.put("one", 1); // throwing on this line might be better but it's too late to change

    assertThrows(IllegalArgumentException.class, () -> builder.buildOrThrow());
  }

  public void testBuildKeepingLast_allowsOverwrite() {
    Builder<Integer, String> builder =
        new Builder<Integer, String>()
            .put(1, "un")
            .put(2, "deux")
            .put(70, "soixante-dix")