Fix race condition in tst_QDBusConnection::pendingCallWhenDisconnected

The test sent a message and hoped that the "delete server" would cause
the server object in the QDBusConnectionManager thread be deleted before
it could receive and process the message. That's racy, because on some
CI machines, it did and then sent back an error reply indicating the
object sought was not found.

Instead, let's use a child process that we can kill to make it exit at
the right time.

I've chosen to use dbus-daemon itself, because that lets us test the
actual conditions that triggered the original bug: the daemon getting
killed during a desktop session shutdown on Linux.

Change-Id: I87e17314d8b24ae983b1fffd1454483aea87c921
Reviewed-by: Tony Sarajärvi <[email protected]>

tests/auto/dbus/qdbusconnection/tst_qdbusconnection.cpp

@@ -40,6 +40,11 @@
 #include <QtTest/QtTest>
 #include <QtDBus/QtDBus>
 
+#ifdef Q_OS_UNIX
+#  include <sys/types.h>
+#  include <signal.h>
+#endif
+
 void MyObject::method(const QDBusMessage &msg)
 {
     path = msg.path();
@@ -1357,23 +1362,39 @@ void tst_QDBusConnection::callVirtualObjectLocal()
 
 void tst_QDBusConnection::pendingCallWhenDisconnected()
 {
+#ifdef QT_NO_PROCESS
+    QSKIP("Test requires QProcess");
+#else
     if (!QCoreApplication::instance())
         QSKIP("Test requires a QCoreApplication");
 
-    QDBusServer *server = new QDBusServer;
-    QDBusConnection con = QDBusConnection::connectToPeer(server->address(), "disconnect");
-    QTestEventLoop::instance().enterLoop(2);
-    QVERIFY(con.isConnected());
-    QDBusMessage message = QDBusMessage::createMethodCall("", "/", QString(), "method");
-    QDBusPendingCall reply = con.asyncCall(message);
+    QProcess daemon;
+    daemon.start("dbus-daemon", QStringList() << "--session" << "--nofork" << "--print-address");
+    QVERIFY2(daemon.waitForReadyRead(2000),
+             "Daemon didn't print its address in time; error: \"" + daemon.errorString().toLocal8Bit() +
+             "\"; stderr:\n" + daemon.readAllStandardError());
 
-    delete server;
+    QString address = QString::fromLocal8Bit(daemon.readAll().trimmed());
+    QDBusConnection con = QDBusConnection::connectToBus(address, "disconnect");
+    QVERIFY2(con.isConnected(), (con.lastError().name() + ": " + con.lastError().message()).toLocal8Bit());
 
-    QTestEventLoop::instance().enterLoop(2);
+    // confirm we're connected and we're alone in this bus
+    QCOMPARE(con.baseService(), QString(":1.0"));
+
+    // kill the bus
+    daemon.terminate();
+    daemon.waitForFinished();
+
+    // send something, which we should get an error with
+    QDBusMessage message = QDBusMessage::createMethodCall("org.freedesktop.DBus", "/", QString(), "ListNames");
+    QDBusPendingCall reply = con.asyncCall(message);
+
+    reply.waitForFinished();
     QVERIFY(!con.isConnected());
     QVERIFY(reply.isFinished());
     QVERIFY(reply.isError());
-    QVERIFY(reply.error().type() == QDBusError::Disconnected);
+    QCOMPARE(reply.error().type(), QDBusError::Disconnected);
+#endif
 }
 
 QString MyObject::path;