doc: add docs for QTest::createTouchDevice()

Task-number: QTBUG-44030
Change-Id: I4bb6a0d0a257cf94883895baebafba70d0cf0f58
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>

src/testlib/doc/snippets/code/src_qtestlib_qtestcase.cpp

@@ -241,17 +241,18 @@ QTest::qWaitForWindowShown(&widget);
 //! [24]
 
 //! [25]
+QTouchDevice *dev = QTest::createTouchDevice();
 QWidget widget;
 
-QTest::touchEvent(&widget)
+QTest::touchEvent(&widget, dev)
     .press(0, QPoint(10, 10));
-QTest::touchEvent(&widget)
+QTest::touchEvent(&widget, dev)
     .stationary(0)
     .press(1, QPoint(40, 10));
-QTest::touchEvent(&widget)
+QTest::touchEvent(&widget, dev)
     .move(0, QPoint(12, 12))
     .move(1, QPoint(45, 5));
-QTest::touchEvent(&widget)
+QTest::touchEvent(&widget, dev)
     .release(0, QPoint(12, 12))
     .release(1, QPoint(45, 5));
 //! [25]

src/testlib/qtestcase.qdoc

@@ -1121,6 +1121,20 @@
     \sa QTest::qWaitForWindowActive(), QTest::qWaitForWindowExposed()
 */
 
+/*!
+    \fn QTest::createTouchDevice()
+    \since 5.8
+
+    Creates a dummy touch device for simulation of touch events.
+
+    The touch device will be registered with the QPA window system interface,
+    and deleted automatically when the QCoreApplication is deleted. So you
+    should typically use createTouchDevice() to initialize a QTouchDevice
+    member variable in your test case class, and use the same instance for all tests.
+
+    \sa QTest::QTouchEventSequence
+*/
+
 /*!
     \class QTest::QTouchEventSequence
     \inmodule QtTest