public void GetDiffExpressions() { var t_CommonExpression = new IdentifierExpression(); var t_State = new ParseState(new Stack <Token>(), new List <IExpression> { t_CommonExpression }); var t_CopyState = new ParseState(new Stack <Token>(), new List <IExpression> { t_CommonExpression, new OperatorExpression() }); var t_Expressions = t_CopyState.DiffExpressions(t_State); t_Expressions.Should().HaveCount(1); t_Expressions.Should().OnlyContain(E => E.GetType() == typeof(OperatorExpression)); }