I've never heard of this but, it sounds interesting lol
I have heard of this and it isn't safe at all nor remotely accurate. Urine has ammonia in it and when ammonia and bleach mix it releases a very toxic gas, and almost always when urine hits bleach it will fiz or foam that's what creates the gas. I had a friend who tried this once in high school, (just for fun, she wasn't pregnant nor did she want to be) and she ended up in the hospital from the gas it created. Sorry didn't mean to scare you just stating the facts.
wow DEFINITELY do not do this. fbifanccr is SO right...urine has ammonia in it and you do NOT want to mix that with bleach, it can be deadly!
Just buy a test.....
If you are pregnant and a few weeks along... a dollar store one would be fine if you're worried about the money.