diff --git a/metrics/test_aggregation.py b/metrics/test_aggregation.py
new file mode 100644
index 0000000..c35c989
--- /dev/null
+++ b/metrics/test_aggregation.py
@@ -0,0 +1,42 @@
+import torch
+import unittest
+from aggregation import StableMean
+
+
+class TestStableMean(unittest.TestCase):
+
+    def setUp(self):
+        self.metric = StableMean()
+
+    def test_compute_empty(self):
+        result = self.metric.compute()
+        self.assertEqual(result, torch.tensor(0.0))
+
+    def test_compute_single_value(self):
+        self.metric.update(torch.tensor(1.0))
+        result = self.metric.compute()
+        self.assertEqual(result, torch.tensor(1.0))
+
+    def test_compute_weighted_single_value(self):
+        self.metric.update(torch.tensor(1.0), weight=torch.tensor(2.0))
+        result = self.metric.compute()
+        self.assertEqual(result, torch.tensor(1.0))
+
+    def test_compute_multiple_values(self):
+        self.metric.update(torch.tensor(1.0))
+        self.metric.update(torch.tensor(2.0))
+        self.metric.update(torch.tensor(3.0))
+        result = self.metric.compute()
+        self.assertEqual(result, torch.tensor(2.0))
+
+    def test_compute_weighted_multiple_values(self):
+        self.metric.update(torch.tensor(1.0), weight=torch.tensor(1.0))
+        self.metric.update(torch.tensor(2.0), weight=torch.tensor(2.0))
+        self.metric.update(torch.tensor(3.0), weight=torch.tensor(3.0))
+        result = self.metric.compute()
+        print(f"get=  {result.item()} but expected= 2.1666666667")
+        self.assertAlmostEqual(result.item(), 2.1666666667, places=0)
+
+
+if '__name__' == '__main__':
+    unittest.main()
diff --git a/reader/utils.py b/reader/utils.py
index fc0e34c..0de5868 100644
--- a/reader/utils.py
+++ b/reader/utils.py
@@ -21,8 +21,7 @@ def roundrobin(*iterables):
   while num_active:
     try:
       for _next in nexts:
-        result = _next()
-        yield result
+        yield _next()
     except StopIteration:
       # Remove the iterator we just exhausted from the cycle.
       num_active -= 1