What is tear test? What do we understand from this test? How?

The tear test determines the force required by a material to undergo complete failure when there is already a crack or tear present in it.

With this test we understand a material's resistance to failure when there is already a crack present.

The material which already has a crack is placed in a tensile testing or universal test machine. So, both sides of the material along the crack are pulled until material failure takes place.