DebugTools: restore usage of external plugins in the CompareImage test.

This was working originally, but got broken when all plugin interfaces
got switched to look for plugins next to the library and not in a
hardcoded install path.

src/Magnum/DebugTools/Test/CompareImageTest.cpp

@@ -1190,7 +1190,7 @@ void CompareImageTest::imageFileExpectedLoadFailed() {
 }
 
 void CompareImageTest::imageFileActualIsCompressed() {
-    PluginManager::Manager<Trade::AbstractImporter> manager;
+    PluginManager::Manager<Trade::AbstractImporter> manager{MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR};
     if(manager.load("AnyImageImporter") < PluginManager::LoadState::Loaded ||
        manager.load("DdsImporter") < PluginManager::LoadState::Loaded)
         CORRADE_SKIP("AnyImageImporter or DdsImporter plugins can't be loaded.");
@@ -1213,7 +1213,7 @@ void CompareImageTest::imageFileActualIsCompressed() {
 }
 
 void CompareImageTest::imageFileExpectedIsCompressed() {
-    PluginManager::Manager<Trade::AbstractImporter> manager;
+    PluginManager::Manager<Trade::AbstractImporter> manager{MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR};
     if(manager.load("AnyImageImporter") < PluginManager::LoadState::Loaded ||
        manager.load("DdsImporter") < PluginManager::LoadState::Loaded)
         CORRADE_SKIP("AnyImageImporter or DdsImporter plugins can't be loaded.");
@@ -1389,7 +1389,7 @@ void CompareImageTest::imageToFileExpectedLoadFailed() {
 }
 
 void CompareImageTest::imageToFileExpectedIsCompressed() {
-    PluginManager::Manager<Trade::AbstractImporter> manager;
+    PluginManager::Manager<Trade::AbstractImporter> manager{MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR};
     if(manager.load("AnyImageImporter") < PluginManager::LoadState::Loaded ||
        manager.load("DdsImporter") < PluginManager::LoadState::Loaded)
             CORRADE_SKIP("AnyImageImporter or DdsImporter plugins can't be loaded.");
@@ -1528,7 +1528,7 @@ void CompareImageTest::fileToImageActualLoadFailed() {
 }
 
 void CompareImageTest::fileToImageActualIsCompressed() {
-    PluginManager::Manager<Trade::AbstractImporter> manager;
+    PluginManager::Manager<Trade::AbstractImporter> manager{MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR};
     if(manager.load("AnyImageImporter") < PluginManager::LoadState::Loaded ||
        manager.load("DdsImporter") < PluginManager::LoadState::Loaded)
             CORRADE_SKIP("AnyImageImporter or DdsImporter plugins can't be loaded.");

src/Magnum/DebugTools/Test/configure.h.cmake

@@ -30,3 +30,17 @@
 #define DEBUGTOOLS_TEST_DIR "${DEBUGTOOLS_TEST_DIR}"
 #define SCREENSHOTTEST_SAVE_DIR "${SCREENSHOTTEST_SAVE_DIR}"
 #define COMPAREIMAGETEST_SAVE_DIR "${COMPAREIMAGETEST_SAVE_DIR}"
+
+#ifdef CORRADE_TARGET_WINDOWS
+#ifdef CORRADE_IS_DEBUG_BUILD
+#define MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/${MAGNUM_PLUGINS_IMPORTER_DEBUG_BINARY_INSTALL_DIR}"
+#else
+#define MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/${MAGNUM_PLUGINS_IMPORTER_RELEASE_BINARY_INSTALL_DIR}"
+#endif
+#else
+#ifdef CORRADE_IS_DEBUG_BUILD
+#define MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/${MAGNUM_PLUGINS_IMPORTER_DEBUG_LIBRARY_INSTALL_DIR}"
+#else
+#define MAGNUM_PLUGINS_IMPORTER_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/${MAGNUM_PLUGINS_IMPORTER_RELEASE_LIBRARY_INSTALL_DIR}"
+#endif
+#endif