I have a set of JUnit tests for my ClientHandler class. Each test works fine when run alone, but when run together, they randomly throw a java.io.IOException: Read end dead.
I have already tried to:

1. Synchronized each method to prevent concurrency issues.
2. Added a latch to the ClientHandler’s run() method.
3. Tested the ClientHandler in a real-world simulation where it works fine.

Below is an example of one of these tests; the others are very similar, differing only in which method they verify.

@Test
    public synchronized void placeMsgTest() throws Exception {
        ClientHandlerTestSetup setup = setupClientHandler();
        ObjectOutputStream toClientHandler = setup.toClientHandler();
        ControllerInterface mockController = setup.controller();

        LightPlacement fakePlacement = new LightPlacement(new Position(0, 0), new LightCard(0), CardFace.FRONT);
        ClientMsg placeMsg = new PlaceMsg(fakePlacement);
        toClientHandler.writeObject(placeMsg);
        toClientHandler.flush();
        Thread.sleep(10);

        verify(mockController, times(1)).place(fakePlacement);
    }

    private synchronized ClientHandlerTestSetup setupClientHandler() throws IOException {
        PipedInputStream inputPipe = new PipedInputStream();
        PipedOutputStream outputPipe = new PipedOutputStream();
        inputPipe.connect(outputPipe);

        ByteArrayOutputStream fromClientHandler = new ByteArrayOutputStream();

        Socket mockClient = mock(Socket.class);
        when(mockClient.getOutputStream()).thenReturn(fromClientHandler);
        when(mockClient.getInputStream()).thenReturn(inputPipe);

        when(mockClient.getInetAddress()).thenReturn(null);

        VirtualView mockView = mock(VirtualView.class);
        ControllerInterface mockController = mock(ControllerInterface.class);

        ClientHandler clientHandler = new ClientHandler(mockClient);
        Thread clientHandlerThread = new Thread(clientHandler, "testedClientHandler");
        clientHandlerThread.start();
        clientHandler.setOwner(mockView);
        clientHandler.setController(mockController);

        ObjectOutputStream toClientHandler = new ObjectOutputStream(outputPipe);
        return new ClientHandlerTestSetup(clientHandler, toClientHandler, mockController);
    }

    private record ClientHandlerTestSetup(ClientHandler clientHandler, ObjectOutputStream toClientHandler, ControllerInterface controller) {}