Add a test for sum/trace/prod 2023.12 upcasting behavior

Author: asmeurer

array_api_strict/tests/test_statistical_functions.py

@@ -0,0 +1,27 @@
+import pytest
+
+import array_api_strict as xp
+
+@pytest.mark.parametrize('func_name', ['sum', 'prod', 'trace'])
+def test_sum_prod_trace_2023_12(func_name):
+    # sum, prod, and trace were changed in 2023.12 to not upcast floating-point dtypes
+    # with dtype=None
+    if func_name == 'trace':
+        func = getattr(xp.linalg, func_name)
+    else:
+        func = getattr(xp, func_name)
+
+    a_real = xp.asarray([[1., 2.], [3., 4.]], dtype=xp.float32)
+    a_complex = xp.asarray([[1., 2.], [3., 4.]], dtype=xp.complex64)
+    a_int = xp.asarray([[1, 2], [3, 4]], dtype=xp.int32)
+
+    assert func(a_real).dtype == xp.float64
+    assert func(a_complex).dtype == xp.complex128
+    assert func(a_int).dtype == xp.int64
+
+    with pytest.warns(UserWarning):
+        xp.set_array_api_strict_flags(api_version='2023.12')
+
+    assert func(a_real).dtype == xp.float32
+    assert func(a_complex).dtype == xp.complex64
+    assert func(a_int).dtype == xp.int64