Is it worth buying a domain name when testing a niche ?

I was considering trying a new niche, and I was wondering if it was worth buying a new domain name just to try it out ?
It's not about spending $8 but more about the thought of it being wasted in case the niche wouldn't eventually be worth it.
I know I could just use WordPress.com, blogspot or Tumbler, but i really like to control everything under a self hosted wordpress installation.
So would a subdomain would be viable or do you guys have any particular advice on that ?

See original post by tobalsan