Ported test_print/test_printobject/test_3mf from upstream Slic3r, thanks @lordofhyphens

tests/libslic3r/CMakeLists.txt

@@ -1,6 +1,7 @@
 get_filename_component(_TEST_NAME ${CMAKE_CURRENT_LIST_DIR} NAME)
 add_executable(${_TEST_NAME}_tests 
 	${_TEST_NAME}_tests.cpp
+	test_3mf.cpp
 	test_geometry.cpp
 	test_polygon.cpp
 	)

tests/libslic3r/test_3mf.cpp

@@ -0,0 +1,20 @@
+#include <catch2/catch.hpp>
+
+#include "libslic3r/Model.hpp"
+#include "libslic3r/Format/3mf.hpp"
+
+using namespace Slic3r;
+
+SCENARIO("Reading 3mf file") {
+    GIVEN("umlauts in the path of the file") {
+        Slic3r::Model model;
+        WHEN("3mf model is read") {
+        	std::string path = std::string(TEST_DATA_DIR) + "/test_3mf/Geräte/Büchse.3mf";
+        	DynamicPrintConfig config;
+            bool ret = Slic3r::load_3mf(path.c_str(), &config, &model, false);
+            THEN("load should succeed") {
+                REQUIRE(ret);
+            }
+        }
+    }
+}