Added simple init test for material manager

tests/TestMaterialManager.py

@@ -0,0 +1,18 @@
+from unittest.mock import MagicMock, patch
+
+from cura.Machines.MaterialManager import MaterialManager
+
+
+mocked_registry = MagicMock()
+material_1 = {"id": "test", "GUID":"TEST!", "base_file": "base_material", "definition": "fdmmachine", "approximate_diameter": 3}
+material_2 = {"id": "base_material", "GUID":"TEST2!", "base_file": "test", "definition": "fdmmachine", "approximate_diameter": 3}
+mocked_registry.findContainersMetadata = MagicMock(return_value = [material_1, material_2])
+
+def test_initialize(application):
+    # Just test if the simple loading works
+    with patch("UM.Application.Application.getInstance", MagicMock(return_value=application)):
+        manager = MaterialManager(mocked_registry)
+    manager.initialize()
+    # Double check that we actually got some material nodes
+    assert manager.getMaterialGroup("base_material").name == "base_material"
+    assert manager.getMaterialGroup("test").name == "test"