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

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

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

    val out1 = stream1.getSink().buffer()
    out1.write(ByteArray(Settings.DEFAULT_INITIAL_WINDOW_SIZE))
    out1.flush()

    // Check that we've filled the window for both the stream and also the connection.
    assertThat(connection.writeBytesTotal)
      .isEqualTo(Settings.DEFAULT_INITIAL_WINDOW_SIZE.toLong())
    assertThat(connection.writeBytesMaximum)