There are many ways to know if you've got a great idea on your hands. Do your colleagues like it, is the research positive, is there a clear gap in the market, are investors interested? Yet the best way to see if you have a winning plan is to ask your mum.
If your mum glazes over when you describe your new ventures then don't bother. If she responds by saying, "Oh, that's really cool," then push on!
The nicest thing about The Mum Test is if your business doesn't end up working out, you know your mum will still love you. This isn't necessarily the case with investors!
My mum has always supported me through thick and thin, and there is nothing more valuable than the support of your family. Plus, she certainly knows a good business idea when she sees it - she's had a fair few good ones herself.