Stabilize tst_QSpinBox::sizeHint()

The test function used to flake on Linux occasionally.
8e6ede7 provided a fix. While it
seemed to work, further analysis has shown that the root cause is
event sequence in case of multiple paint events.

This patch re-engineers the test function:

1. Allocate test widget on the stack instead of the heap.
2. Send layout requests posted by QHBoxLayout constructor and
QLayout::addWidget() before showing the widget.
3. Remove calls to QCoreApplication::processEvents().
They are unnessecary, because
- the size hint request counter is supposed to increase (by any number)
- QTRY_VERIFY processes events anyway until the counter increases or it
times out.

Pick-to: 6.5 6.4 6.2
Change-Id: I54998483725cbdd4899ba6f5469d7dae0980ab1d
Reviewed-by: Friedemann Kleint <[email protected]>

tests/auto/widgets/widgets/qspinbox/tst_qspinbox.cpp

@@ -1152,34 +1152,32 @@ class sizeHint_SpinBox : public QSpinBox
 
 void tst_QSpinBox::sizeHint()
 {
-    QWidget *widget = new QWidget;
-    QHBoxLayout *layout = new QHBoxLayout(widget);
-    widget->setLayout(layout);
+    QWidget widget;
+    QHBoxLayout *layout = new QHBoxLayout(&widget);
+
     sizeHint_SpinBox *spinBox = new sizeHint_SpinBox;
     layout->addWidget(spinBox);
-    widget->show();
-    QVERIFY(QTest::qWaitForWindowExposed(widget));
+    // Make sure all layout requests posted by the QHBoxLayout constructor and addWidget
+    // are processed before the widget is shown
+    QCoreApplication::sendPostedEvents(&widget, QEvent::LayoutRequest);
+    widget.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&widget));
 
     // Prefix
     spinBox->sizeHintRequests = 0;
     spinBox->setPrefix(QLatin1String("abcdefghij"));
-    qApp->processEvents();
     QTRY_VERIFY(spinBox->sizeHintRequests > 0);
 
     // Suffix
     spinBox->sizeHintRequests = 0;
     spinBox->setSuffix(QLatin1String("abcdefghij"));
-    qApp->processEvents();
     QTRY_VERIFY(spinBox->sizeHintRequests > 0);
 
     // Range
     spinBox->sizeHintRequests = 0;
     spinBox->setRange(0, 1234567890);
     spinBox->setValue(spinBox->maximum());
-    qApp->processEvents();
     QTRY_VERIFY(spinBox->sizeHintRequests > 0);
-
-    delete widget;
 }
 
 void tst_QSpinBox::taskQTBUG_5008_textFromValueAndValidate()