SimpleTreeModel: Add a test

Add a test running QAbstractItemModelTester on the model.

Change-Id: I6ea5d34308357409b9a13eb0271392c8d171addd
Reviewed-by: Kai Köhne <kai.koehne@qt.io>
(cherry picked from commit d9c71b834ccd815b85e9589f21eba1f51c48614a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/widgets/doc/src/simpletreemodel.qdoc

@@ -319,4 +319,20 @@
 
     To ensure that the model works correctly, it is only necessary to
     create instances of \c TreeItem with the correct data and parent item.
+
+    \section1 Testing the model
+
+    Correctly implementing an item model can be challenging. The class
+    \l QAbstractItemModelTester from the \l{Qt Test} module checks for model
+    consistency, like the model index creation and parent-child relationships.
+
+    You can test your model by just passing a model instance to the class
+    constructor, for instance as part of a Qt unit test:
+
+    \snippet itemviews/simpletreemodel/test.cpp 1
+
+    To create a test which can be run using the \c ctest executable,
+    \c add_test() is used:
+
+    \snippet itemviews/simpletreemodel/CMakeLists.txt 1
 */

examples/widgets/itemviews/simpletreemodel/CMakeLists.txt

@@ -10,7 +10,7 @@ endif()
 
 set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/widgets/itemviews/simpletreemodel")
 
-find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets)
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Test Widgets)
 
 qt_standard_project_setup()
 
@@ -48,3 +48,29 @@ install(TARGETS simpletreemodel
     BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
     LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
 )
+
+#! [1]
+# Unit Test
+
+include(CTest)
+
+qt_add_executable(simpletreemodel_tester
+    test.cpp
+    treeitem.cpp treeitem.h
+    treemodel.cpp treemodel.h)
+
+target_link_libraries(simpletreemodel_tester PRIVATE
+    Qt6::Core
+    Qt6::Test
+)
+
+qt_add_resources(simpletreemodel_tester "simpletreemodel"
+    PREFIX
+        "/"
+    FILES
+        ${simpletreemodel_resource_files}
+)
+
+add_test(NAME simpletreemodel_tester
+         COMMAND simpletreemodel_tester)
+#! [1]

examples/widgets/itemviews/simpletreemodel/test.cpp

@@ -0,0 +1,35 @@
+// Copyright (C) 2023 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "treemodel.h"
+
+#include <QObject>
+#include <QAbstractItemModelTester>
+#include <QTest>
+
+using namespace Qt::StringLiterals;
+
+//! [1]
+class TestSimpleTreeModel : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void testTreeModel();
+};
+
+void TestSimpleTreeModel::testTreeModel()
+{
+    constexpr auto fileName = ":/default.txt"_L1;
+    QFile file(fileName);
+    QVERIFY2(file.open(QIODevice::ReadOnly | QIODevice::Text),
+             qPrintable(fileName + " cannot be opened: "_L1 + file.errorString()));
+    TreeModel model(QString::fromUtf8(file.readAll()));
+
+    QAbstractItemModelTester tester(&model);
+}
+
+QTEST_APPLESS_MAIN(TestSimpleTreeModel)
+
+#include "test.moc"
+//! [1]