IELTS -Listening test uses a variety of accents. But the most common accents are the accents prevailing in the five main English-speaking countries i.e. The UK, Australia, Canada, New Zealand and the US. However, the choicest ones are the British and the Australian as IELTS is co-owned by Australian and British entities.
The best way to understand these accents used in IELTS is to listen to as many tests as possible. However, watching television channels like BBC news can make a lot of difference. Likewise watching Australian channels would also help, as Australian accents are also very commonly used in the IELTS. Watching Hollywood movies can also help as they give you better understanding of conversational English