Add test for Timedelta hash invariance

Author: harahu

pandas/tests/scalar/timedelta/test_arithmetic.py

@@ -6,9 +6,13 @@
     timedelta,
 )
 import operator
+import sys
+from typing import Hashable
 
 import numpy as np
 import pytest
+from hypothesis import given
+from hypothesis.strategies import integers
 
 from pandas.errors import OutOfBoundsTimedelta
 
@@ -1143,6 +1147,72 @@ def test_compare_unknown_type(self, val):
         with pytest.raises(TypeError, match=msg):
             t < val
 
+    @given(integers(min_value=-sys.maxsize - 1, max_value=sys.maxsize))
+        def test_hash_invariant(value: int) -> None:
+        """Reproducing GH#44504
+    
+        See: https://github.com/pandas-dev/pandas/issues/44504
+        """
+    
+        # See: UnitChoices in pandas/_libs/tslibs/timedeltas.pyi
+        unit_choices = (
+            "W",
+            "w",
+            "D",
+            "d",
+            "days",
+            "day",
+            "hours",
+            "hour",
+            "hr",
+            "h",
+            "m",
+            "minute",
+            "min",
+            "minutes",
+            "t",
+            "s",
+            "seconds",
+            "sec",
+            "second",
+            "ms",
+            "milliseconds",
+            "millisecond",
+            "milli",
+            "millis",
+            "l",
+            "us",
+            "microseconds",
+            "microsecond",
+            "µs",
+            "micro",
+            "micros",
+            "u",
+            "ns",
+            "nanoseconds",
+            "nano",
+            "nanos",
+            "nanosecond",
+            "n",
+        )
+    
+        def _hash_invariance_upheld(v1: Hashable, v2: Hashable) -> bool:
+            if v1 != v2:
+                return True
+    
+            # See: https://docs.python.org/3/glossary.html#term-hashable
+            # Hashable objects which compare equal must have the same hash value.
+            return hash(v1) == hash(v2)
+    
+        for unit in unit_choices:
+            pd_td = Timedelta(value, unit)
+            np_td = np.timedelta64(value)
+    
+            try:
+                assert _hash_invariance_upheld(pd_td, np_td)
+            except AssertionError:
+                pytest.xfail("pd.Timedelta violates hash invariant (GH#44504).")
+
 
 def test_ops_notimplemented():
     class Other: