QCanBus: Receive an error message from createDevice()

[ChangeLog] Before, createDevice() could only return
nullptr if anything goes wrong. Now, an optional textual
error description can be returned.

Task-number: QTBUG-53642
Change-Id: Ie097e5c63096ae6a6fb9a798e4a8f23219cf1cfb
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>

2 files changed, 16 insertions, 3 deletions

diff --git a/tests/auto/plugins/genericcanbus/main.cpp b/tests/auto/plugins/genericcanbus/main.cpp
index 3fc6225..d482c3b 100644
--- a/tests/auto/plugins/genericcanbus/main.cpp
+++ b/tests/auto/plugins/genericcanbus/main.cpp
@@ -50,9 +50,15 @@ class GenericBusPlugin : public QObject, public QCanBusFactory
     Q_INTERFACES(QCanBusFactory)
 
 public:
-    QCanBusDevice *createDevice(const QString &interfaceName) const
+    QCanBusDevice *createDevice(const QString &interfaceName,
+                                QString *errorMessage) const
     {
-        Q_UNUSED(interfaceName)
+        if (interfaceName == QStringLiteral("invalid")) {
+            if (errorMessage)
+                *errorMessage = tr("No such interface: '%1'").arg(interfaceName);
+
+            return nullptr;
+        }
         auto device = new DummyBackend();
         return device;
     }
diff --git a/tests/auto/qcanbus/tst_qcanbus.cpp b/tests/auto/qcanbus/tst_qcanbus.cpp
index 08047e8..63f98cc 100644
--- a/tests/auto/qcanbus/tst_qcanbus.cpp
+++ b/tests/auto/qcanbus/tst_qcanbus.cpp
@@ -85,12 +85,19 @@ void tst_QCanBus::plugins()
 
 void tst_QCanBus::createDevice()
 {
+    QString error, error2;
     QCanBusDevice *dummy = bus->createDevice("generic", "unused");
     QCanBusDevice *dummy2 = bus->createDevice("generic", "unused");
-    QCanBusDevice *faulty = bus->createDevice("faulty", "faulty");
+    QCanBusDevice *faulty = bus->createDevice("generic", "invalid", &error);
+    QCanBusDevice *faulty2 = bus->createDevice("faulty", "faulty", &error2);
     QVERIFY(dummy);
     QVERIFY(dummy2);
+
     QVERIFY(!faulty);
+    QCOMPARE(error, tr("No such interface: 'invalid'"));
+
+    QVERIFY(!faulty2);
+    QCOMPARE(error2, tr("No such plugin: 'faulty'"));
 
     delete dummy;
     delete dummy2;