Fix memory leak in unit tests

The created SDL_Surfaces were not destroyed. Use a smart pointer with custom
deleter to do that.

src/tests/test_dmg_acid2.cpp

@@ -35,22 +35,25 @@ TEST_CASE("dmg_acid2") {
 
     // Convert the framebuffer to an SDL_Surface to save it for convenient comparisons if the tests
     // fail.
-    auto* actual_image = actual_framebuffer.to_surface();
-    SDL_SaveBMP(actual_image, "dmg-acid2-actual.bmp");
+    using unique_surface_t = std::unique_ptr<SDL_Surface, decltype(&SDL_FreeSurface)>;
+    unique_surface_t actual_image{actual_framebuffer.to_surface(), SDL_FreeSurface};
+    SDL_SaveBMP(actual_image.get(), "dmg-acid2-actual.bmp");
 
     // Load the known-good screenshot from a file
-    auto* expected_image = SDL_LoadBMP("recorded-logs/dmg-acid2.bmp");
-    expected_image = SDL_ConvertSurface(expected_image, actual_image->format, 0);
+    const unique_surface_t expected_image_load{SDL_LoadBMP("recorded-logs/dmg-acid2.bmp"),
+                                               SDL_FreeSurface};
+    unique_surface_t expected_image{
+        SDL_ConvertSurface(expected_image_load.get(), actual_image->format, 0), SDL_FreeSurface};
     REQUIRE(expected_image != nullptr);
     Framebuffer<graphics::gb::ColorScreen, constants::SCREEN_RES_WIDTH,
                 constants::SCREEN_RES_HEIGHT>
         result;
-    auto res = SDL_LockSurface(expected_image);
+    auto res = SDL_LockSurface(expected_image.get());
     REQUIRE(res == 0);
     REQUIRE(expected_image->h * expected_image->pitch
             == result.size() * sizeof(graphics::gb::ColorScreen));
     result.take_from(expected_image->pixels);
-    SDL_UnlockSurface(expected_image);
+    SDL_UnlockSurface(expected_image.get());
     // Compare the actual screenshot to the known-good one
     for (size_t x = 0; x < result.width(); ++x) {
         for (size_t y = 0; y < result.height(); ++y) {