Unable to read from socket if data is first written to it

#include <QTcpServer>
#include <QTcpSocket>
#include <QTest>

class TestSocketBug : public QObject
{
    Q_OBJECT

private Q_SLOTS:

    void testBug();
};

void TestSocketBug::testBug()
{
    QTcpServer server;
    QVERIFY(server.listen(QHostAddress::LocalHost));

    QTcpSocket clientSocket;
    clientSocket.connectToHost(server.serverAddress(), server.serverPort());
    QTRY_COMPARE(clientSocket.state(), QAbstractSocket::ConnectedState);

    QTcpSocket *serverSocket = server.nextPendingConnection();
    serverSocket->write("test");
    serverSocket->close();

    clientSocket.write("something");

    QTRY_COMPARE(clientSocket.bytesAvailable(), 4);
}

QTEST_MAIN(TestSocketBug)
#include "TestSocketBug.moc"

cmake_minimum_required(VERSION 2.8.11)
project(socketbug)

set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTOMOC ON)

find_package(Qt5Network REQUIRED)
find_package(Qt5Test REQUIRED)

add_executable(socketbug TestSocketBug.cpp)
qt5_use_modules(socketbug Network Test)