TST: Extract a helper function to test for reference cycles

This also means we can now test that our test is actually able to detect the type of failure we expect

Trying to give myself some tools to debug the failure at https://github.com/numpy/numpy/pull/10882/files#r180813166

1 files changed, 28 insertions, 1 deletions

diff --git a/numpy/testing/tests/test_utils.py b/numpy/testing/tests/test_utils.py
index 35f81d8a7..52726db6e 100644
--- a/numpy/testing/tests/test_utils.py
+++ b/numpy/testing/tests/test_utils.py
@@ -14,7 +14,7 @@ from numpy.testing import (
     assert_raises, assert_warns, assert_no_warnings, assert_allclose,
     assert_approx_equal, assert_array_almost_equal_nulp, assert_array_max_ulp,
     clear_and_catch_warnings, suppress_warnings, assert_string_equal, assert_,
-    tempdir, temppath,
+    tempdir, temppath, assert_no_gc_cycles, HAS_REFCOUNT
     )
 
 
@@ -1360,3 +1360,30 @@ def test_clear_and_catch_warnings_inherit():
         warnings.simplefilter('ignore')
         warnings.warn('Some warning')
     assert_equal(my_mod.__warningregistry__, {})
+
+
+@pytest.mark.skipif(not HAS_REFCOUNT, reason="Python lacks refcounts")
+def test_assert_no_gc_cycles():
+
+    def no_cycle():
+        b = []
+        b.append([])
+        return b
+
+    with assert_no_gc_cycles():
+        no_cycle()
+
+    assert_no_gc_cycles(no_cycle)
+
+    def make_cycle():
+        a = []
+        a.append(a)
+        a.append(a)
+        return a
+
+    with assert_raises(AssertionError):
+        with assert_no_gc_cycles():
+            make_cycle()
+
+    with assert_raises(AssertionError):
+        assert_no_gc_cycles(make_cycle)