def test_matrix_is_not_invertible(self):
matrix = Matrix([[-4, 2, -2, -3], [9, 6, 2, 6], [0, -5, 1, -5],
[0, 0, 0, 0]])
assert not matrix.is_invertible()
def test_matrix_is_invertible(self):
matrix = Matrix([[6, 4, 4, 4], [5, 5, 7, 6], [4, -9, 3, -7],
[9, 1, 7, -6]])
assert matrix.is_invertible()
