How i can check that a registry cleaner is actually clean the all invalid registry entries.?

I scaned my computers registry from a registry cleaner, but I m in doubt that is it really cleaning the invalid registryies or not. I think that it is not compeletly scanning all registry entries. One more think I create a invalid registry in "regeditor" but it is not showing me that invalid registry. So how i can chk abt this "is my registry cleaner is working fine or not"