Add a TestHelpers_ file for each platform

So we don't have too much ifdefed stuff that's only for tests in
the main files.

src/qtquick/TestHelpers_qtquick.cpp

@@ -0,0 +1,55 @@
+/*
+  This file is part of KDDockWidgets.
+
+  SPDX-FileCopyrightText: 2020-2022 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+  Author: Sérgio Martins <sergio.martins@kdab.com>
+
+  SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+
+  Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+
+#include "KDDockWidgets.h"
+#include "Platform_qtquick.h"
+
+#include "views/View_qtquick.h"
+#include <QApplication> // TODO: Make it QGuiApplication
+#include <QQmlEngine>
+#include <QQuickStyle>
+#include <QQuickItem>
+
+using namespace KDDockWidgets;
+
+#ifdef DOCKS_DEVELOPER_MODE
+
+Platform_qtquick::Platform_qtquick(int argc, char *argv[])
+    : Platform_qt(argc, argv)
+{
+    new QApplication(argc, argv);
+    init();
+}
+
+void Platform_qtquick::tests_initPlatform_impl()
+{
+    Platform_qt::tests_initPlatform_impl();
+
+    QQuickStyle::setStyle(QStringLiteral("Material")); // so we don't load KDE plugins
+    m_qmlEngine = new QQmlEngine();
+}
+
+void Platform_qtquick::tests_deinitPlatform_impl()
+{
+    delete m_qmlEngine;
+    Platform_qt::tests_deinitPlatform_impl();
+}
+
+std::shared_ptr<ViewWrapper> Platform_qtquick::tests_createView(std::shared_ptr<ViewWrapper> parent)
+{
+    auto parentItem = parent ? Views::asQQuickItem(parent.get()) : nullptr;
+    auto newItem = new QQuickItem(parentItem);
+
+    auto wrapper = new Views::ViewWrapper_qtquick(newItem);
+    return std::shared_ptr<ViewWrapper>(wrapper);
+}
+
+#endif