TST: Add regression test for pyarrow datetime merge with duplicates (GH#61926) (pandas-dev#62592)

Author: G26karthik

pandas/tests/reshape/merge/test_merge.py

@@ -3097,3 +3097,27 @@ def test_merge_categorical_key_recursion():
         right.astype("float64"), on="key", how="outer"
     )
     tm.assert_frame_equal(result, expected)
+
+
+def test_merge_pyarrow_datetime_duplicates():
+    # GH#61926
+    pytest.importorskip("pyarrow")
+
+    t = pd.date_range("2025-07-06", periods=3, freq="h")
+    df1 = DataFrame({"time": t, "val1": [1, 2, 3]})
+    df1 = df1.convert_dtypes(dtype_backend="pyarrow")
+
+    df2 = DataFrame({"time": t.repeat(2), "val2": [10, 20, 30, 40, 50, 60]})
+    df2 = df2.convert_dtypes(dtype_backend="pyarrow")
+
+    result = merge(df1, df2, on="time", how="left")
+
+    expected = DataFrame(
+        {
+            "time": t.repeat(2),
+            "val1": [1, 1, 2, 2, 3, 3],
+            "val2": [10, 20, 30, 40, 50, 60],
+        }
+    )
+    expected = expected.convert_dtypes(dtype_backend="pyarrow")
+    tm.assert_frame_equal(result, expected)