val response1 = call1.execute()
    val response2 = call2.execute()
    assertThat(response1.body.source().readUtf8(3)).isEqualTo("ABC")
    assertThat(response2.body.source().readUtf8(3)).isEqualTo("GHI")
    assertThat(response1.body.source().readUtf8(3)).isEqualTo("DEF")
    assertThat(response2.body.source().readUtf8(3)).isEqualTo("JKL")
    val c0e0 = server.takeRequest()
    assertThat(c0e0.connectionIndex).isEqualTo(0)

    index: Int,
  ) = cacheDir / "$key.$index.tmp"

  private fun readFile(file: Path): String =
    filesystem.read(file) {
      readUtf8()
    }

  private fun readFileOrNull(file: Path): String? =
    try {
      filesystem.read(file) {
        readUtf8()
      }
    } catch (_: FileNotFoundException) {
      null
    }

  fun writeFile(
    file: Path,

    connection.writePingAndAwaitPong()
    assertThat(stream.takeHeaders()).isEqualTo(headersOf("a", "android"))
    val source = stream.source.buffer()
    assertThat(source.readUtf8(5)).isEqualTo("robot")
    stream.sink.close()
    assertThat(connection.openStreamCount()).isEqualTo(0)

    // Verify the peer received what was expected.
    val synStream = peer.takeFrame()