test(gui): add BitmapFactory DPI-aware SVG rendering tests (#189)

Three tests for the loadPixmap() DPI fix:
- pixmapFromSvg(content, size) renders at the exact requested size
- getMaximumDPR() returns >= 1.0
- pixmap() loaded from an SVG file has correct devicePixelRatio and
  physical size matching 64 * DPR

tests/src/Gui/BitmapFactory.cpp

@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+
+#include <gtest/gtest.h>
+
+#include <QApplication>
+#include <QDir>
+#include <QFile>
+#include <QTemporaryDir>
+
+#include <Gui/BitmapFactory.h>
+
+#include <src/App/InitApplication.h>
+
+
+namespace
+{
+
+// Minimal valid SVG used as test icon
+constexpr const char* kTestSvg =
+    R"(<svg xmlns="http://www.w3.org/2000/svg" width="64" height="64")"
+    R"( viewBox="0 0 64 64"><rect width="64" height="64" fill="#ff0000"/></svg>)";
+
+}  // namespace
+
+
+class BitmapFactoryTest : public ::testing::Test
+{
+protected:
+    static void SetUpTestSuite()
+    {
+        tests::initApplication();
+
+        // QPixmap and QSvgRenderer require a QGuiApplication.
+        // gtest_main does not create one, so we construct it here.
+        if (!QApplication::instance()) {
+            static int argc = 1;
+            static char arg0[] = "Gui_tests_run";
+            static char* argv[] = {arg0, nullptr};
+            static QApplication app(argc, argv);
+        }
+    }
+};
+
+
+// pixmapFromSvg(content, size) renders at the exact requested size
+TEST_F(BitmapFactoryTest, PixmapFromSvgContentRendersAtRequestedSize)
+{
+    QByteArray svg(kTestSvg);
+    QSize requested(48, 48);
+    QPixmap px = Gui::BitmapFactory().pixmapFromSvg(svg, requested);
+
+    ASSERT_FALSE(px.isNull());
+    EXPECT_EQ(px.width(), 48);
+    EXPECT_EQ(px.height(), 48);
+}
+
+// getMaximumDPR returns at least 1.0
+TEST_F(BitmapFactoryTest, MaximumDPRIsAtLeastOne)
+{
+    qreal dpr = Gui::BitmapFactoryInst::getMaximumDPR();
+    EXPECT_GE(dpr, 1.0);
+}
+
+// pixmap() loaded from an SVG file has correct devicePixelRatio and physical size
+TEST_F(BitmapFactoryTest, PixmapFromSvgFileHasCorrectDPR)
+{
+    // Write a test SVG to a temporary directory
+    QTemporaryDir tmpDir;
+    ASSERT_TRUE(tmpDir.isValid());
+
+    QString svgPath = tmpDir.path() + QDir::separator() + "test-dpi-icon.svg";
+    QFile file(svgPath);
+    ASSERT_TRUE(file.open(QFile::WriteOnly | QFile::Text));
+    file.write(kTestSvg);
+    file.close();
+
+    // Add the temp dir as a search path and load via pixmap()
+    Gui::BitmapFactory().addPath(tmpDir.path());
+    QPixmap px = Gui::BitmapFactory().pixmap("test-dpi-icon");
+
+    ASSERT_FALSE(px.isNull());
+
+    qreal expectedDpr = Gui::BitmapFactoryInst::getMaximumDPR();
+    EXPECT_DOUBLE_EQ(px.devicePixelRatio(), expectedDpr);
+
+    // Physical size should be 64 * dpr
+    int expectedPhysical = static_cast<int>(64 * expectedDpr);
+    EXPECT_EQ(px.width(), expectedPhysical);
+    EXPECT_EQ(px.height(), expectedPhysical);
+
+    Gui::BitmapFactory().removePath(tmpDir.path());
+}

tests/src/Gui/CMakeLists.txt

@@ -3,6 +3,7 @@
 # Standard C++ GTest tests
 add_executable(Gui_tests_run
         Assistant.cpp
+        BitmapFactory.cpp
         Camera.cpp
         StyleParameters/StyleParametersApplicationTest.cpp
         StyleParameters/ParserTest.cpp