diff --git a/test/cubic.test.py b/test/cubic.test.py
index 4ccbac3..3b1adff 100755
--- a/test/cubic.test.py
+++ b/test/cubic.test.py
@@ -12,7 +12,7 @@ from interp.grid.simplex import contains
 def exact_func(X):
   x = X[0]
   y = X[0]
-  return 1 - math.sin((x-0.5)**2 + (y-0.5)**2)
+  return 1 + x + y
 
 class TestSequenceFunctions(unittest.TestCase):
   def setUp(self):