for (int i = 0; i < num; i++) {
        rest[i] = partsArray[i + 2];
      }

      assertThat(joiner.join(partsArray[0], partsArray[1], rest)).isEqualTo(expected);

      StringBuilder sb3 = new StringBuilder().append('x');
      joiner.appendTo(sb3, partsArray[0], partsArray[1], rest);
      assertThat(sb3.toString()).isEqualTo("x" + expected);
    }
  }