Fix self-reference in test causing recursion depth error (#1600)

Author: nspope

stdpopsim/dfe.py

@@ -1,7 +1,7 @@
 """
 Common infrastructure for specifying DFEs.
 """
-# import numpy as np
+
 import textwrap
 import attr
 import collections.abc

tests/test_dfes.py

@@ -717,8 +717,9 @@ def make_dfe(self, name):
 
     def test_register_qc(self):
         dfe = self.make_dfe("test")
-        dfe.register_qc(dfe)
-        assert dfe.qc_dfe == dfe
+        dfe_two = self.make_dfe("test")
+        dfe.register_qc(dfe_two)
+        assert dfe.qc_dfe == dfe_two
 
     def test_already_registered(self):
         dfe = self.make_dfe("test")