[test][libraryeditor] Check that the editor produces valid json

beat/editor/test/test_libraryeditor.py

@@ -38,6 +38,7 @@ class TestLibraryEditor:
         editor.load_json(reference_json)
 
         assert editor.dump_json() == reference_json
+        assert editor.is_valid()
 
     def test_load_and_dump_wrong(self, qtbot, test_prefix):
         faulty_json = {"description": "test", "uses": {"alias": "test/dummy/1"}}
@@ -48,3 +49,4 @@ class TestLibraryEditor:
         editor.load_json(faulty_json)
 
         assert editor.dump_json() == reference_json
+        assert editor.is_valid()