diff --git a/src/shamira/tests/test_gf256.py b/src/shamira/tests/test_gf256.py
--- a/src/shamira/tests/test_gf256.py
+++ b/src/shamira/tests/test_gf256.py
@@ -30,7 +30,9 @@ class TestGF256(TestCase):
 			self.assertEqual(evaluate([a0, a1, a2, a3], 1), a0^a1^a2^a3)  # polynomial at 1 == sum of coefficients
 
 	def test_get_constant_coef(self):
-		self.assertEqual(get_constant_coef((1, 1), (2, 2), (3, 3)), 0)
+		weights = compute_weights((1, 2, 3))
+		ys = (1, 2, 3)
+		self.assertEqual(get_constant_coef(weights, ys), 0)
 
 		random.seed(17)
 		random_matches = 0
@@ -55,7 +57,10 @@ class TestGF256(TestCase):
 		coefs = [random.randint(0, 255) for i in range(k)]
 		points = [(j, evaluate(coefs, j)) for j in range(1, 256)]
 		random.shuffle(points)
-		return (get_constant_coef(*points[:m]), coefs[0])
+
+		(xs, ys) = zip(*points[:m])
+		weights = compute_weights(xs)
+		return (get_constant_coef(weights, ys), coefs[0])
 
 
 if __name__=='__main__':