diff --git a/tests/auto/gui/image/qimageiohandler/CMakeLists.txt b/tests/auto/gui/image/qimageiohandler/CMakeLists.txt
index 9fbd9c9b9f4..6f9f1ce7ea6 100644
--- a/tests/auto/gui/image/qimageiohandler/CMakeLists.txt
+++ b/tests/auto/gui/image/qimageiohandler/CMakeLists.txt
@@ -11,9 +11,22 @@ if(NOT QT_BUILD_STANDALONE_TESTS AND NOT QT_BUILDING_QT)
     find_package(Qt6BuildInternals REQUIRED COMPONENTS STANDALONE_TEST)
 endif()
 
+file(GLOB_RECURSE test_data_glob
+    RELATIVE ${CMAKE_CURRENT_SOURCE_DIR}
+    images/*)
+
+list(APPEND test_data ${test_data_glob})
+
+add_subdirectory(plugin)
+
 qt_internal_add_test(tst_qimageiohandler
     SOURCES
         tst_qimageiohandler.cpp
+        pluginlog.h
     LIBRARIES
         Qt::Gui
+        TestImagePlugin
+    TESTDATA ${test_data}
 )
+
+add_dependencies(tst_qimageiohandler TestImagePlugin)
diff --git a/tests/auto/gui/image/qimageiohandler/images/black.bar b/tests/auto/gui/image/qimageiohandler/images/black.bar
new file mode 100644
index 00000000000..41e34fd7798
Binary files /dev/null and b/tests/auto/gui/image/qimageiohandler/images/black.bar differ
diff --git a/tests/auto/gui/image/qimageiohandler/images/black.bmp b/tests/auto/gui/image/qimageiohandler/images/black.bmp
new file mode 100644
index 00000000000..41e34fd7798
Binary files /dev/null and b/tests/auto/gui/image/qimageiohandler/images/black.bmp differ
diff --git a/tests/auto/gui/image/qimageiohandler/images/blue b/tests/auto/gui/image/qimageiohandler/images/blue
new file mode 100644
index 00000000000..a6c5d80d5aa
--- /dev/null
+++ b/tests/auto/gui/image/qimageiohandler/images/blue
@@ -0,0 +1 @@
+BLUE
diff --git a/tests/auto/gui/image/qimageiohandler/images/cyan.gif b/tests/auto/gui/image/qimageiohandler/images/cyan.gif
new file mode 100644
index 00000000000..840da8ceb62
Binary files /dev/null and b/tests/auto/gui/image/qimageiohandler/images/cyan.gif differ
diff --git a/tests/auto/gui/image/qimageiohandler/images/green.foo b/tests/auto/gui/image/qimageiohandler/images/green.foo
new file mode 100644
index 00000000000..a5b73ed2e94
--- /dev/null
+++ b/tests/auto/gui/image/qimageiohandler/images/green.foo
@@ -0,0 +1 @@
+green
diff --git a/tests/auto/gui/image/qimageiohandler/images/red.png b/tests/auto/gui/image/qimageiohandler/images/red.png
new file mode 100644
index 00000000000..f24fc29aa68
--- /dev/null
+++ b/tests/auto/gui/image/qimageiohandler/images/red.png
@@ -0,0 +1 @@
+RED
diff --git a/tests/auto/gui/image/qimageiohandler/images/white.foo b/tests/auto/gui/image/qimageiohandler/images/white.foo
new file mode 100644
index 00000000000..8085a0d4aa7
Binary files /dev/null and b/tests/auto/gui/image/qimageiohandler/images/white.foo differ
diff --git a/tests/auto/gui/image/qimageiohandler/images/yellow.jpg b/tests/auto/gui/image/qimageiohandler/images/yellow.jpg
new file mode 100644
index 00000000000..d1ed081dfb9
--- /dev/null
+++ b/tests/auto/gui/image/qimageiohandler/images/yellow.jpg
@@ -0,0 +1 @@
+yellow
diff --git a/tests/auto/gui/image/qimageiohandler/plugin/CMakeLists.txt b/tests/auto/gui/image/qimageiohandler/plugin/CMakeLists.txt
new file mode 100644
index 00000000000..e0aaddf2406
--- /dev/null
+++ b/tests/auto/gui/image/qimageiohandler/plugin/CMakeLists.txt
@@ -0,0 +1,17 @@
+# Copyright (C) 2024 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+#####################################################################
+## TestImagePlugin:
+#####################################################################
+
+qt_add_plugin(TestImagePlugin
+    STATIC
+    OUTPUT_NAME qtestimageplugin
+    PLUGIN_TYPE imageformats
+    main.cpp
+    ../pluginlog.h
+)
+
+qt_autogen_tools_initial_setup(TestImagePlugin)
+target_link_libraries(TestImagePlugin PRIVATE Qt::Core Qt::Gui)
diff --git a/tests/auto/gui/image/qimageiohandler/plugin/main.cpp b/tests/auto/gui/image/qimageiohandler/plugin/main.cpp
new file mode 100644
index 00000000000..5a1289c2abd
--- /dev/null
+++ b/tests/auto/gui/image/qimageiohandler/plugin/main.cpp
@@ -0,0 +1,89 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
+
+#include <qimageiohandler.h>
+#include <qcoreapplication.h>
+#include "../pluginlog.h"
+
+class TestImagePlugin : public QImageIOPlugin
+{
+    Q_OBJECT
+    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QImageIOHandlerFactoryInterface" FILE "plugin.json")
+
+public:
+    QImageIOPlugin::Capabilities capabilities(QIODevice *device, const QByteArray &format) const override;
+    QImageIOHandler *create(QIODevice *device, const QByteArray &format = QByteArray()) const override;
+};
+
+class MyPngHandler : public QImageIOHandler
+{
+public:
+    bool canRead() const override
+    {
+        if (canRead(device())) {
+            setFormat(device()->peek(1).isUpper() ? "png" : "foo");
+            return true;
+        }
+        return false;
+    }
+
+    bool read(QImage *image) override
+    {
+        QColor col = QColor::fromString(device()->readAll().simplified());
+        if (col.isValid()) {
+            QImage img(32, 32, QImage::Format_RGB32);
+            img.fill(col);
+            *image = img;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    static bool canRead(QIODevice *device)
+    {
+        return device ? QColor::isValidColorName(device->peek(16).simplified()) : false;
+    }
+};
+
+
+QImageIOPlugin::Capabilities TestImagePlugin::capabilities(QIODevice *device, const QByteArray &format) const
+{
+    if (format == "png" || format == "foo" || format == "gif") {
+        PluginLog::append("formatname-matched");
+        return (format == "gif") ? CanWrite : CanRead;
+    }
+
+    Capabilities cap;
+    if (!format.isEmpty()) {
+        PluginLog::append("formatname-unmatched");
+        return cap;
+    }
+
+    if (!device->isOpen())
+        return cap;
+
+    if (device->isReadable()) {
+        if (MyPngHandler::canRead(device)) {
+            PluginLog::append("contents-matched");
+            cap |= CanRead;
+        } else {
+            PluginLog::append("contents-unmatched");
+        }
+    }
+
+    if (device->isWritable())
+        cap |= CanWrite;
+
+    return cap;
+}
+
+QImageIOHandler *TestImagePlugin::create(QIODevice *device, const QByteArray &format) const
+{
+    QImageIOHandler *handler = new MyPngHandler;
+    handler->setDevice(device);
+    handler->setFormat(format);
+    return handler;
+}
+
+#include "main.moc"
diff --git a/tests/auto/gui/image/qimageiohandler/plugin/plugin.json b/tests/auto/gui/image/qimageiohandler/plugin/plugin.json
new file mode 100644
index 00000000000..be5282af2fa
--- /dev/null
+++ b/tests/auto/gui/image/qimageiohandler/plugin/plugin.json
@@ -0,0 +1,4 @@
+{
+    "Keys": [ "png", "foo", "gif" ],
+    "MimeTypes": [ "image/png", "image/foo", "image/gif" ]
+}
diff --git a/tests/auto/gui/image/qimageiohandler/pluginlog.h b/tests/auto/gui/image/qimageiohandler/pluginlog.h
new file mode 100644
index 00000000000..140a54c4029
--- /dev/null
+++ b/tests/auto/gui/image/qimageiohandler/pluginlog.h
@@ -0,0 +1,22 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
+
+#ifndef PLUGINLOG_H
+#define PLUGINLOG_H
+
+#include <QCoreApplication>
+#include <QVariant>
+
+class PluginLog {
+public:
+    static QStringList get() { return qApp->property(testProp).toStringList(); }
+    static void set(const QStringList &log) { qApp->setProperty(testProp, log); }
+    static void clear() { set({}); }
+    static void append(const QString &msg) { set(get() << msg); }
+    static int size() { return get().size(); }
+    static QString item(int index) { return get().value(index); }
+private:
+    static constexpr auto testProp = "_q_testimageplugin";
+};
+
+#endif // PLUGINLOG_H
diff --git a/tests/auto/gui/image/qimageiohandler/tst_qimageiohandler.cpp b/tests/auto/gui/image/qimageiohandler/tst_qimageiohandler.cpp
index bd325e185c6..aefc427cac5 100644
--- a/tests/auto/gui/image/qimageiohandler/tst_qimageiohandler.cpp
+++ b/tests/auto/gui/image/qimageiohandler/tst_qimageiohandler.cpp
@@ -6,8 +6,11 @@
 
 #include <qcoreapplication.h>
 #include <qdebug.h>
+#include <qhash.h>
 #include <qimageiohandler.h>
 #include <qfile.h>
+#include <qimagereader.h>
+#include "pluginlog.h"
 
 class tst_QImageIOHandler : public QObject
 {
@@ -16,9 +19,27 @@ Q_OBJECT
 public:
     tst_QImageIOHandler();
     virtual ~tst_QImageIOHandler();
+    static void initMain()
+    {
+        QHashSeed::setDeterministicGlobalSeed();
+    }
 
 private slots:
     void getSetCheck();
+    void hasCustomPluginFormat();
+    void pluginRead_data();
+    void pluginRead();
+    void pluginNoAutoDetection_data();
+    void pluginNoAutoDetection();
+    void pluginDecideFromContent_data();
+    void pluginDecideFromContent();
+    void pluginDetectedFormat_data();
+    void pluginDetectedFormat();
+    void pluginWrongFormat_data();
+    void pluginWrongFormat();
+private:
+    QString m_prefix;
+    QList<QByteArray> m_supportedReadFormats;
 };
 
 class MyImageIOHandler : public QImageIOHandler
@@ -31,6 +52,8 @@ public:
 
 tst_QImageIOHandler::tst_QImageIOHandler()
 {
+    m_prefix = QFINDTESTDATA("images/");
+    m_supportedReadFormats = QImageReader::supportedImageFormats();
 }
 
 tst_QImageIOHandler::~tst_QImageIOHandler()
@@ -51,5 +74,185 @@ void tst_QImageIOHandler::getSetCheck()
     delete var1;
 }
 
+Q_IMPORT_PLUGIN(TestImagePlugin)
+
+void tst_QImageIOHandler::hasCustomPluginFormat()
+{
+    QVERIFY(m_supportedReadFormats.contains("foo"));
+}
+
+void tst_QImageIOHandler::pluginRead_data()
+{
+    QTest::addColumn<QString>("color");
+    QTest::addColumn<QString>("suffix");
+    QTest::addColumn<QStringList>("expectedPluginLog");
+
+    QTest::newRow("testplugin") << "green" << "foo" << QStringList({ "formatname-matched" });
+    QTest::newRow("overridden-builtin") << "red" << "png" << QStringList({ "formatname-matched" });
+    QTest::newRow("builtin") << "black" << "bmp" << QStringList({ "formatname-unmatched" }); //### Should be null
+    QTest::newRow("no-suffix") << "blue" << "" << QStringList({ "contents-matched" });
+    QTest::newRow("wrong-suffix") << "yellow" << "jpg" << QStringList({ "contents-matched" });
+    QTest::newRow("unknown-suffix") << "black" << "bar" << QStringList({ "formatname-unmatched", "contents-unmatched" });
+    if (m_supportedReadFormats.contains("jpeg"))
+        QTest::newRow("wrong-suffix2") << "white" << "foo" << QStringList({ "formatname-matched" });
+    if (m_supportedReadFormats.contains("gif"))
+        QTest::newRow("plugin-writeonly") << "cyan" << "gif" << QStringList();
+}
+
+void tst_QImageIOHandler::pluginRead()
+{
+    QFETCH(QString, color);
+    QFETCH(QString, suffix);
+    QFETCH(QStringList, expectedPluginLog);
+
+    PluginLog::clear();
+    QString filePath = m_prefix + color + (suffix.isEmpty() ? "" : "." + suffix);
+    QImage img(filePath);
+    QCOMPARE(PluginLog::size(), expectedPluginLog.size());
+    for (int i = 0; i < PluginLog::size(); i++)
+        QCOMPARE(PluginLog::item(i), expectedPluginLog.value(i));
+    QVERIFY(!img.isNull());
+    QCOMPARE(img.pixelColor(0, 0), QColor(color));
+}
+
+void tst_QImageIOHandler::pluginNoAutoDetection_data()
+{
+    QTest::addColumn<QString>("color");
+    QTest::addColumn<QString>("suffix");
+    QTest::addColumn<QStringList>("expectedPluginLog");
+    QTest::addColumn<bool>("expectedSuccess");
+
+    QTest::newRow("testplugin") << "green" << "foo" << QStringList({ "formatname-matched" }) << true;
+    QTest::newRow("overridden-builtin") << "red" << "png" << QStringList({ "formatname-matched" }) << true;
+    QTest::newRow("builtin") << "black" << "bmp" << QStringList() << true;
+    QTest::newRow("no-suffix") << "blue" << "" << QStringList() << false;
+    QTest::newRow("wrong-suffix") << "yellow" << "jpg" << QStringList() << false;
+    QTest::newRow("unknown-suffix") << "black" << "bar" << QStringList() << false;
+    QTest::newRow("wrong-suffix2") << "white" << "foo" << QStringList({ "formatname-matched" }) << false;
+    QTest::newRow("plugin-writeonly") << "cyan" << "gif" << QStringList() << true;
+}
+
+void tst_QImageIOHandler::pluginNoAutoDetection()
+{
+    QFETCH(QString, color);
+    QFETCH(QString, suffix);
+    QFETCH(QStringList, expectedPluginLog);
+    QFETCH(bool, expectedSuccess);
+
+    QString filePath = m_prefix + color + (suffix.isEmpty() ? "" : "." + suffix);
+    {
+        // Confirm that the file suffix is ignored, i.e. nothing happens if no format is set
+        PluginLog::clear();
+        QImageReader r(filePath);
+        r.setAutoDetectImageFormat(false);
+        QImage img = r.read();
+        QVERIFY(img.isNull());
+        QCOMPARE(PluginLog::size(), 0);
+    }
+
+    PluginLog::clear();
+    QImageReader r(filePath, suffix.toLatin1());
+    r.setAutoDetectImageFormat(false);
+    QImage img = r.read();
+
+    QCOMPARE(PluginLog::size(), expectedPluginLog.size());
+    for (int i = 0; i < PluginLog::size(); i++)
+        QCOMPARE(PluginLog::item(i), expectedPluginLog.value(i));
+    QCOMPARE(!img.isNull(), expectedSuccess);
+    if (expectedSuccess)
+        QCOMPARE(img.pixelColor(0, 0), QColor(color));
+}
+
+void tst_QImageIOHandler::pluginDecideFromContent_data()
+{
+    QTest::addColumn<QString>("color");
+    QTest::addColumn<QString>("suffix");
+    QTest::addColumn<QStringList>("expectedPluginLog");
+
+    QTest::newRow("testplugin") << "green" << "foo" << QStringList({ "contents-matched" });
+    QTest::newRow("overridden-builtin") << "red" << "png" << QStringList({ "contents-matched" });
+    QTest::newRow("builtin") << "black" << "bmp" << QStringList({ "contents-unmatched" });
+    QTest::newRow("no-suffix") << "blue" << "" << QStringList({ "contents-matched" });
+    QTest::newRow("wrong-suffix") << "yellow" << "jpg" << QStringList({ "contents-matched" });
+    QTest::newRow("unknown-suffix") << "black" << "bar" << QStringList({ "contents-unmatched" });
+    if (m_supportedReadFormats.contains("jpeg"))
+        QTest::newRow("wrong-suffix2") << "white" << "foo" << QStringList();
+}
+
+void tst_QImageIOHandler::pluginDecideFromContent()
+{
+    QFETCH(QString, color);
+    QFETCH(QString, suffix);
+    QFETCH(QStringList, expectedPluginLog);
+
+    QString filePath = m_prefix + color + (suffix.isEmpty() ? "" : "." + suffix);
+    PluginLog::clear();
+    QImageReader r(filePath, suffix.toLatin1());
+    r.setDecideFormatFromContent(true);
+    QImage img = r.read();
+
+    QCOMPARE(PluginLog::size(), expectedPluginLog.size());
+    for (int i = 0; i < PluginLog::size(); i++)
+        QCOMPARE(PluginLog::item(i), expectedPluginLog.value(i));
+    QVERIFY(!img.isNull());
+    QCOMPARE(img.pixelColor(0, 0), QColor(color));
+}
+
+void tst_QImageIOHandler::pluginDetectedFormat_data()
+{
+    QTest::addColumn<QString>("color");
+    QTest::addColumn<QString>("suffix");
+    QTest::addColumn<QString>("fileFormat");
+
+    QTest::newRow("testplugin") << "green" << "foo" << "foo";
+    QTest::newRow("overridden-builtin") << "red" << "png" << "png";
+    QTest::newRow("builtin") << "black" << "bmp" << "bmp";
+    QTest::newRow("no-suffix") << "blue" << "" << "png";
+    QTest::newRow("wrong-suffix") << "yellow" << "jpg" << "foo";
+    QTest::newRow("unknown-suffix") << "black" << "bar" << "bmp";
+    if (m_supportedReadFormats.contains("jpeg"))
+        QTest::newRow("wrong-suffix2") << "white" << "foo" << "jpeg";
+    if (m_supportedReadFormats.contains("gif"))
+        QTest::newRow("plugin-writeonly") << "cyan" << "gif" << "gif";
+}
+
+void tst_QImageIOHandler::pluginDetectedFormat()
+{
+    QFETCH(QString, color);
+    QFETCH(QString, suffix);
+    QFETCH(QString, fileFormat);
+
+    QString filePath = m_prefix + color + (suffix.isEmpty() ? "" : "." + suffix);
+    QCOMPARE(QImageReader::imageFormat(filePath), fileFormat.toLatin1());
+}
+
+void tst_QImageIOHandler::pluginWrongFormat_data()
+{
+    QTest::addColumn<QString>("color");
+    QTest::addColumn<QString>("suffix");
+    QTest::addColumn<QString>("forceFormat");
+
+    QTest::newRow("testplugin") << "green" << "foo" << "bmp";
+    QTest::newRow("overridden-builtin") << "red" << "png" << "bmp";
+    QTest::newRow("builtin") << "black" << "bmp" << "foo";
+    QTest::newRow("no-suffix") << "blue" << "" << "bmp";
+    QTest::newRow("wrong-suffix") << "yellow" << "jpg" << "bmp";
+    QTest::newRow("unknown-suffix") << "black" << "bar" << "foo";
+    QTest::newRow("wrong-suffix2") << "white" << "foo" << "bmp";
+}
+
+void tst_QImageIOHandler::pluginWrongFormat()
+{
+    QFETCH(QString, color);
+    QFETCH(QString, suffix);
+    QFETCH(QString, forceFormat);
+
+    PluginLog::clear();
+    QString filePath = m_prefix + color + (suffix.isEmpty() ? "" : "." + suffix);
+    QImage img(filePath, forceFormat.toLatin1());
+    QVERIFY(img.isNull());
+}
+
 QTEST_MAIN(tst_QImageIOHandler)
+
 #include "tst_qimageiohandler.moc"