boundary = "simple boundary",
        source = Buffer().writeUtf8(multipart),
      )

    parts.nextPart()!!
    val partMno = parts.nextPart()!!
    assertThat(partMno.body.readUtf8()).isEqualTo("mnop")

    assertThat(parts.nextPart()).isNull()
  }

  @Test fun `cannot read part after calling nextPart`() {
    val multipart =
      """
      |--simple boundary
      |
      |abcd
      |efgh

    ```kotlin
    val response: Response = call.execute()
    val multipartReader = MultipartReader(response.body!!)

    multipartReader.use {
      while (true) {
        val part = multipartReader.nextPart() ?: break
        process(part.headers, part.body)
      }
    }
    ```

 *  New: `MediaType.parameter()` gets a parameter like `boundary` from a media type like
    `multipart/mixed; boundary="abc"`.