The primary and the simplest test to check whether or not the milk has gone bad is to smell it
Milk is a thin and smooth liquid If it has yellow colour than pure white, it is a sign that the milk is not pure
The colour of pure and fresh milk is clean white
Make sure, if the milk is sitting out, it is only at the recommended 39 degree F
As the old saying goes, it is better to be safe than sorry. It is always better to toss away the spoilt milk, than to be at the risk of food poisoning.
If the milk happens to have lumps or is odd in texture and colour, it is not safe to consume