That was terrible advice. And even though it is from the movie blow it is a real coke test.
Tell me, do you have a melt point device at home? This test is only going to be accurate if you have one and this isn't a common house hold item.
Not to mention that you are an idiot by saying that cocaine melting at 140 degrees would be okay, 150 better, 160 good etc.
That's not how the test even works, you could have a cut that has a low melting point and melts at like 70 degrees and still have good cocaine, the actual cocaine isn't going to melt until 195 degrees regardless (i believe this is the correct melting point). So if all your powder melts at 140 degrees, or 150, 160, 170, it means you don't have real cocaine numb nuts.
And the test works on range, carefully watching what amount of powder melts before you reach the 195 degrees (and when, to identify the cuts), so you can't just use a small bump to do the test anyways you'd have to use multiple decent sized samples. (wasting them)
And once again nobody is going to have melt point device at home so YOUR advice was terrible because the OP is gonna try doing it in his oven or some shit which would not be remotely accurate.
I simply gave the OP some advice that one could perform in a few seconds to get a general idea of how pure their product is.