server.processNextFrame()
    // Not closed until close reply is received.
    assertThat(client.closed).isFalse()

    // Manually write an invalid masked close frame.
    server.sink.write("888760b420bb635c68de0cd84f".decodeHex()).emit()
    client.processNextFrame() // Detects error, disconnects immediately since close already sent.
    client.webSocket!!.finishReader()
    assertThat(client.closed).isTrue()