My friend’s girl tested positive for pregnancy yesterday but she is disputing the results as she says she’s on her menses. Is is reliable to do a pregnancy test during menstruation?

I’ve seen pregnancy tests in dollar stores, and even though they say they’re accurate, I have to wonder. If you look at pregnancy tests at stores like Target or Wal-Mart, they’re more expensive. So are pregnancy tests from dollar stores reliable, or are the bigger stores just ripping us off? Is it better to use a more expensive brand of pregnancy test, or will a dollar store brand give you just as accurate a result?
Thanks guys, this is my first time taking a pregnancy test!

How long after conception would a pregnancy test be reliable?
Note: after conception, please dont tell me about ovulation or days from period or due date of periods or anything.
Thanks!

I need to buy one by tomorrow.
I’m Malaysian anyway.
Please recommend me some affordable and reliable pregnancy test.
We have Watson and Guardian shops here.