You should have posted a link to it.
Also I'm happy to see this, this is what every thread was like back in my "browsing" days, so cool.
Next, there are many ways to tell, depending on just what it's laced with.. coke there'll be white powder at the bottom of the bag (same with heroin, but maybe a bit brown), laced with acid or something (but wtf) you wouldn't notice, but who'd do it? lol.

Just get a reliable supplier.