MAINT,TST: Avoid small positive integers in refcount test

This hopefully makes the test less susceptible to errors, but
we have to use small "singleton" integers for the test to work.

It is not clear that this will actually fix the issue always.
If the issue crops up again, we should simply remove all manual
asserts and rely on `pytest-leaks` as a leak checker.

Closes gh-17381

1 files changed, 16 insertions, 12 deletions

diff --git a/numpy/core/tests/test_dtype.py b/numpy/core/tests/test_dtype.py
index 8fe859919..585b24976 100644
--- a/numpy/core/tests/test_dtype.py
+++ b/numpy/core/tests/test_dtype.py
@@ -723,26 +723,30 @@ class TestStructuredObjectRefcounting:
     def test_structured_object_indexing(self, shape, index, items_changed,
                                         dt, pat, count, singleton):
         """Structured object reference counting for advanced indexing."""
-        zero = 0
-        one = 1
+        # Use two small negative values (should be singletons, but less likely
+        # to run into race-conditions).  This failed in some threaded envs
+        # When using 0 and 1.  If it fails again, should remove all explicit
+        # checks, and rely on `pytest-leaks` reference count checker only.
+        val0 = -4
+        val1 = -5
 
-        arr = np.zeros(shape, dt)
+        arr = np.full(shape, val0, dt)
 
         gc.collect()
-        before_zero = sys.getrefcount(zero)
-        before_one = sys.getrefcount(one)
+        before_val0 = sys.getrefcount(val0)
+        before_val1 = sys.getrefcount(val1)
         # Test item getting:
         part = arr[index]
-        after_zero = sys.getrefcount(zero)
-        assert after_zero - before_zero == count * items_changed
+        after_val0 = sys.getrefcount(val0)
+        assert after_val0 - before_val0 == count * items_changed
         del part
         # Test item setting:
-        arr[index] = one
+        arr[index] = val1
         gc.collect()
-        after_zero = sys.getrefcount(zero)
-        after_one = sys.getrefcount(one)
-        assert before_zero - after_zero == count * items_changed
-        assert after_one - before_one == count * items_changed
+        after_val0 = sys.getrefcount(val0)
+        after_val1 = sys.getrefcount(val1)
+        assert before_val0 - after_val0 == count * items_changed
+        assert after_val1 - before_val1 == count * items_changed
 
     @pytest.mark.parametrize(['dt', 'pat', 'count', 'singleton'],
                              iter_struct_object_dtypes())