public void combines_the_list_of_all_errors()
        {
            var graph = new FixtureStructure("Math");
            graph.AddStructure("key1", new StubGrammarStructure().AddError("error1"));
            graph.AddStructure("key2", new StubGrammarStructure().AddError("error1").AddError("error 2"));

            graph.AllErrors().Count().ShouldEqual(3);
        }