This in one of those tricky questions that doesn't have a right answer .... it really depends on the industry and what the norm is. So design companys for example often have a very casual dress policy. As an assessor, my advice would always be to wear a suit and look smart for an interview. However, if you are unsure there is no harm in calling the company to ask them what the dress code for the interview is.

As an aside, I once did an assessment assignment working for an Australian surf company - the candidate called ahead of time to ask what they should wear and I advised them to dress in a suit. The interview arrived, so did I and the candidate both dressed in business suits and the manager arrived in surf shorts and flip flops ...!

Good Luck!