Add autotest for thumbnails

Thumbnailing is complex code that isn't easy to manually test given the caching mechanism and variety in input data

Add a basic autotest that generates previews for a file and compares them to an expected file

Currently only for png and jpg images, but to be extended to other formats/scenarios

thumbnail/CMakeLists.txt

+if (BUILD_TESTING)
+    add_subdirectory(autotests)
+endif()
+
 add_definitions(-DTRANSLATION_DOMAIN=\"kio5_thumbnail\")
 
 remove_definitions(-DQT_NO_CAST_FROM_ASCII)

thumbnail/autotests/CMakeLists.txt

+# allow coercing cstring to qstring, easier to write
+remove_definitions(-DQT_NO_CAST_FROM_ASCII)
+
+find_package(Qt${QT_MAJOR_VERSION}Test ${QT_MIN_VERSION} CONFIG REQUIRED)
+
+include(ECMAddTests)
+
+ecm_add_tests(
+    thumbnailtest.cpp
+    LINK_LIBRARIES
+        Qt::Test
+        KF5::KIOWidgets
+)

thumbnail/autotests/thumbnailtest.cpp

+/*
+    SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+    SPDX-FileCopyrightText: 2022 Nicolas Fella <nicolas.fella@gmx.de>
+*/
+
+#include <QSignalSpy>
+#include <QStandardPaths>
+#include <QTest>
+
+#include <KIO/PreviewJob>
+
+class ThumbnailTest : public QObject
+{
+    Q_OBJECT
+private Q_SLOTS:
+
+    void testThumbnail_data()
+    {
+        QTest::addColumn<QString>("inputFile");
+        QTest::addColumn<QString>("expectedThumbnail");
+        QTest::addColumn<qreal>("dpr");
+
+        QTest::addRow("png") << "cherry_tree.png"
+                             << "cherry_tree_thumb.png" << 1.0;
+
+        QTest::addRow("png_dpr2") << "cherry_tree.png"
+                                  << "cherry_tree_thumb@2.png" << 2.0;
+
+        QTest::addRow("jpg") << "boxes.jpg"
+                             << "boxes_thumb.png" << 1.0;
+
+        QTest::addRow("jpg_dpr2") << "boxes.jpg"
+                                  << "boxes_thumb@2.png" << 2.0;
+
+        QTest::addRow("jpg_embedded_thumbnail") << "castle.jpg"
+                                                << "castle_thumb.png" << 1.0;
+    }
+
+    void testThumbnail()
+    {
+        QFETCH(QString, inputFile);
+        QFETCH(QString, expectedThumbnail);
+        QFETCH(qreal, dpr);
+
+        QStandardPaths::setTestModeEnabled(true);
+        qputenv("KIOSLAVE_ENABLE_TESTMODE", "1"); // ensure the ioslaves call QStandardPaths::setTestModeEnabled too
+
+        // wipe thumbnail cache so we always start clean
+        QDir cacheDir(QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation));
+        cacheDir.removeRecursively();
+
+        QString path = QFINDTESTDATA("data/" + inputFile);
+
+        KFileItemList items;
+        items.append(KFileItem(QUrl::fromLocalFile(path)));
+
+        QStringList enabledPlugins{"imagethumbnail", "jpegthumbnail"};
+        auto *job = KIO::filePreview(items, QSize(128, 128), &enabledPlugins);
+        job->setDevicePixelRatio(dpr);
+
+        connect(job, &KIO::PreviewJob::gotPreview, this, [path, expectedThumbnail, dpr](const KFileItem &item, const QPixmap &preview) {
+            QCOMPARE(item.url(), QUrl::fromLocalFile(path));
+
+            QImage expectedImage;
+            expectedImage.load(QFINDTESTDATA("data/" + expectedThumbnail));
+            expectedImage.setDevicePixelRatio(dpr);
+
+            QCOMPARE(preview.toImage(), expectedImage);
+        });
+
+        QSignalSpy failedSpy(job, &KIO::PreviewJob::failed);
+        QSignalSpy gotPreviewSpy(job, &KIO::PreviewJob::gotPreview);
+        QSignalSpy resultSpy(job, &KIO::PreviewJob::result);
+
+        gotPreviewSpy.wait();
+        resultSpy.wait();
+
+        QVERIFY(failedSpy.empty());
+    }
+};
+
+QTEST_MAIN(ThumbnailTest)
+
+#include "thumbnailtest.moc"