Added test to check list states elements are deleted (even when refer…

…enced, and hence not automatically garbage collected). Fixed failing test (want to check list state, but assigned Tensor)

tests/unittests/bases/test_metric.py

@@ -124,11 +124,17 @@ class B(DummyListMetric):
     metric = B()
     assert isinstance(metric.x, list)
     assert len(metric.x) == 0
-    metric.x = tensor(5)
+    metric.x = [tensor(5)]
     metric.reset()
     assert isinstance(metric.x, list)
     assert len(metric.x) == 0
 
+    metric = B()
+    metric.x = [1, 2, 3]
+    reference = metric.x  # prevents garbage collection
+    metric.reset()
+    assert len(reference) == 0  # check list state is freed
+
 
 def test_reset_compute():
     """Test that `reset`+`compute` methods works as expected."""