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/qtwidgets/TestHelpers_qtwidgets.cpp

@@ -0,0 +1,54 @@
+/*
+  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_qtwidgets.h"
+#include "views/ViewWrapper_qtwidgets.h"
+#include "views/View_qtwidgets.h"
+
+#include <QStyleFactory>
+#include <QApplication>
+#include <QWidget>
+
+using namespace KDDockWidgets;
+
+#ifdef DOCKS_DEVELOPER_MODE
+
+Platform_qtwidgets::Platform_qtwidgets(int argc, char *argv[])
+    : Platform_qt(argc, argv)
+{
+    qputenv("KDDOCKWIDGETS_SHOW_DEBUG_WINDOW", "");
+    new QApplication(argc, argv);
+    qApp->setStyle(QStyleFactory::create(QStringLiteral("fusion")));
+    init();
+}
+
+void Platform_qtwidgets::tests_initPlatform_impl()
+{
+    Platform_qt::tests_initPlatform_impl();
+}
+
+void Platform_qtwidgets::tests_deinitPlatform_impl()
+{
+    Platform_qt::tests_deinitPlatform_impl();
+}
+
+std::shared_ptr<ViewWrapper> Platform_qtwidgets::tests_createView(std::shared_ptr<ViewWrapper> parent)
+{
+    QWidget *parentWidget = Views::View_qtwidgets<QWidget>::asQWidget(parent.get());
+
+    auto newWidget = new QWidget(parentWidget);
+    auto wrapper = new Views::ViewWrapper_qtwidgets(newWidget);
+
+    return std::shared_ptr<ViewWrapper>(wrapper);
+}
+
+#endif