ENH: add a test that result_type does not depend on the order of arguments

Author: ev-br

array_api_tests/hypothesis_helpers.py

@@ -10,7 +10,7 @@
 from hypothesis import assume, reject
 from hypothesis.strategies import (SearchStrategy, booleans, composite, floats,
                                    integers, just, lists, none, one_of,
-                                   sampled_from, shared, builds, nothing)
+                                   sampled_from, shared, builds, nothing, permutations)
 
 from . import _array_module as xp, api_version
 from . import array_helpers as ah
@@ -148,6 +148,13 @@ def mutually_promotable_dtypes(
     return one_of(strats).map(tuple)
 
 
+@composite
+def pair_of_mutually_promotable_dtypes(draw, max_size=2, *, dtypes=dh.all_dtypes):
+    sample = draw(mutually_promotable_dtypes( max_size, dtypes=dtypes))
+    permuted = draw(permutations(sample))
+    return sample, permuted
+
+
 class OnewayPromotableDtypes(NamedTuple):
     input_dtype: DataType
     result_dtype: DataType

array_api_tests/test_data_type_functions.py

@@ -208,7 +208,17 @@ def test_isdtype(dtype, kind):
     assert out == expected, f"{out=}, but should be {expected} [isdtype()]"
 
 
-@given(hh.mutually_promotable_dtypes(None))
-def test_result_type(dtypes):
-    out = xp.result_type(*dtypes)
-    ph.assert_dtype("result_type", in_dtype=dtypes, out_dtype=out, repr_name="out")
+class TestResultType:
+    @given(dtypes=hh.mutually_promotable_dtypes(None))
+    def test_result_type(self, dtypes):
+        out = xp.result_type(*dtypes)
+        ph.assert_dtype("result_type", in_dtype=dtypes, out_dtype=out, repr_name="out")
+
+    @given(pair=hh.pair_of_mutually_promotable_dtypes(None))
+    def test_shuffled(self, pair):
+        """Test that result_type is insensitive to the order of arguments."""
+        s1, s2 = pair
+        out1 = xp.result_type(*s1)
+        out2 = xp.result_type(*s2)
+        assert out1 == out2
+