fun onePartRequired() {
    assertFailsWith<IllegalStateException> {
      MultipartBody.Builder().build()
    }.also { expected ->
      assertThat(expected.message)
        .isEqualTo("Multipart body must have at least one part.")
    }
  }

  @Test
  fun singlePart() {
    val expected =
      """
      |--123
      |
      |Hello, World!
      |--123--
      |
      """.trimMargin().replace("\n", "\r\n")