I heard that one common method of testing the accused witches was to tie a sack full of stones to the witches ankles then chuck them in the lake. If they floated they were witches. If not... youre still screwed.

Virtually none. At least no testing that would pass as a viable way to determine if someone was a witch. The witch hysteria came about at the surface level as a result of wild behavior from "bewitched" girls, but on a deeper level the Puritan community was undergoing a lot of turmoil at the time and felt that they had incurred God's wrath. The witchhunt was a way of scapegoating people who were supposedly a cause of this. A great way to ruin your enemy or get rid of the villag weirdo was to accuse them of being a witch. They would then be determined to be a witch through "witness testimony" and "evidence examination" and other proceedings worthy of the quotes of sarcasm. In reality there were no tests given, it was all based on heresay, just a manipulative match of pointing fingers that imprisoned or hung a lot of innocent people.

Sir Bedevere: There are ways of telling whether she is a witch. Peasant 1: Are there? Oh well, tell us. Sir Bedevere: Tell me. What do you do with witches? Peasant 1: Burn them. Sir Bedevere: And what do you burn, apart from witches? Sir Bedevere: There are ways of telling whether she is a witch. Peasant 1: Are there? Oh well, tell us. Sir Bedevere: Tell me. What do you do with witches? Peasant 1: Burn them. Sir Bedevere: And what do you burn, apart from witches? Peasant 1: More witches. Peasant 2: Wood. Sir Bedevere: Good. Now, why do witches burn? Peasant 3: ...because they're made of... wood? Sir Bedevere: Good. So how do you tell whether she is made of wood? Peasant 1: Build a bridge out of her. Sir Bedevere: But can you not also build bridges out of stone? Peasant 1: Oh yeah. Sir Bedevere: Does wood sink in water? Peasant 1: No, no, it floats!... It floats! Throw her into the pond! Sir Bedevere: No, no. What else floats in water? Peasant 1: Bread. Peasant 2: Apples. Peasant 3: Very small rocks. Peasant 1: Cider. Peasant 2: Gravy. Peasant 3: Cherries. Peasant 1: Mud. Peasant 2: Churches. Peasant 3: Lead! Lead! King Arthur: A Duck. Sir Bedevere: ...Exactly. So, logically... Peasant 1: If she weighed the same as a duck... she's made of wood. Sir Bedevere: And therefore... Peasant 2: ...A witch!

in all reality the salem witch trials did use this duck test. Monty python took this information and used it for a cheap sham of a travesty of a hollywood hoax. 17 of the 22 accused between February 1692 and May 1693 were found guilty and therefore hung. The Idea was that if the accused weighed more than a duck she was made of wood, and would then float, making her a witch.