A different approach to make the test deterministic

src/sage/categories/fields.py

@@ -93,18 +93,19 @@ def __contains__(self, x):
 
         The following tests against a memory leak fixed in :trac:`13370`. In order
         to prevent non-deterministic deallocation of fields that have been created
-        in other doctests, :trac:`19244` disables garbage collection until we really
-        want it to happen. ::
+        in other doctests, we introduced a strong reference to all previously created
+        uncollected objects in :trac:`19244`. ::
 
             sage: import gc
             sage: _ = gc.collect()
-            sage: gc.disable()
-            sage: n = len([X for X in gc.get_objects() if isinstance(X, sage.rings.finite_rings.integer_mod_ring.IntegerModRing_generic)])
+            sage: permstore = [X for X in gc.get_objects() if isinstance(X, sage.rings.finite_rings.integer_mod_ring.IntegerModRing_generic)]
+            sage: n = len(permstore)
             sage: for i in prime_range(100):
             ....:     R = ZZ.quotient(i)
             ....:     t = R in Fields()
+            sage: len([X for X in gc.get_objects() if isinstance(X, sage.rings.finite_rings.integer_mod_ring.IntegerModRing_generic)]) > n
+            True
             sage: del R
-            sage: gc.enable()
             sage: _ = gc.collect()
             sage: len([X for X in gc.get_objects() if isinstance(X, sage.rings.finite_rings.integer_mod_ring.IntegerModRing_generic)]) - n
             0