parts.nextPart()
    }.also { expected ->
      assertThat(expected).hasMessage("unexpected characters after boundary")
    }
  }

  /** The documentation advises that '-' is the simplest boundary possible. */
  @Test fun `dash boundary`() {
    val multipart =
      """
      |---
      |Content-ID: abc
      |
      |abcd
      |---
      |Content-ID: efg
      |