dedicated tests

Author: jbrockmendel

pandas/core/indexes/datetimes.py

@@ -1108,9 +1108,14 @@ def date_range(
                 td = Timedelta(freq.offset)
                 if abbrev_to_npy_unit(td.unit) > creso:
                     unit = td.unit  # type: ignore[assignment]
-            elif type(freq) is DateOffset and getattr(freq, "nanoseconds", 0) != 0:
-                # e.g. test_freq_dateoffset_with_relateivedelta_nanos
-                unit = "ns"
+            elif type(freq) is DateOffset:
+                if getattr(freq, "nanoseconds", 0) != 0:
+                    # e.g. test_freq_dateoffset_with_relateivedelta_nanos
+                    unit = "ns"
+                elif getattr(freq, "microseconds", 0) != 0 and unit != "ns":
+                    unit = "us"
+                elif getattr(freq, "milliseconds", 0) != 0 and unit not in ["ns", "us"]:
+                    unit = "ms"
 
     dtarr = DatetimeArray._generate_range(
         start=start,

pandas/tests/indexes/datetimes/test_date_range.py

@@ -1814,3 +1814,40 @@ def test_date_range_tzaware_endpoints_accept_nonexistent(self):
             "2015-03-28 01:30", "2015-03-30 01:30", freq="D"
         ).tz_localize(tz, nonexistent="shift_forward")
         tm.assert_index_equal(result, expected)
+
+
+class TestDateRangeUnitInference:
+    def test_date_range_unit_inference_matching_unit(self, unit):
+        start = Timestamp("2025-11-25").as_unit(unit)
+        end = Timestamp("2025-11-26").as_unit(unit)
+
+        dti = date_range(start, end, freq="D")
+        assert dti.unit == unit
+
+    def test_date_range_unit_inference_mismatched_unit(self, unit):
+        start = Timestamp("2025-11-25").as_unit(unit)
+        end = Timestamp("2025-11-26").as_unit("s")
+
+        dti = date_range(start, end, freq="D")
+        assert dti.unit == unit
+
+        dti = date_range(start, end.as_unit("ns"), freq="D")
+        assert dti.unit == "ns"
+
+    def test_date_range_unit_inference_tick(self):
+        start = Timestamp("2025-11-25").as_unit("ms")
+        end = Timestamp("2025-11-26").as_unit("s")
+
+        dti = date_range(start, end, freq="2000000us")
+        assert dti.unit == "us"
+
+        dti = date_range(start, end.as_unit("ns"), freq="2000000us")
+        assert dti.unit == "ns"
+
+    def test_date_range_unit_inference_dateoffset_freq(self):
+        off = DateOffset(microseconds=2_000_000)
+
+        start = Timestamp("2025-11-25").as_unit("ms")
+        end = Timestamp("2025-11-26").as_unit("s")
+        dti = date_range(start, end, freq=off)
+        assert dti.unit == "us"

pandas/tests/indexes/timedeltas/test_timedelta_range.py

@@ -154,3 +154,32 @@ def test_timedelta_range_removed_freq(self, freq_depr, start, end):
         msg = f"Invalid frequency: {freq_depr}"
         with pytest.raises(ValueError, match=msg):
             timedelta_range(start=start, end=end, freq=freq_depr)
+
+
+class TestTimedeltaRangeUnitInference:
+    def test_timedelta_range_unit_inference_matching_unit(self, unit):
+        start = Timedelta(0).as_unit(unit)
+        end = Timedelta(days=1).as_unit(unit)
+
+        tdi = timedelta_range(start, end, freq="D")
+        assert tdi.unit == unit
+
+    def test_timedelta_range_unit_inference_mismatched_unit(self, unit):
+        start = Timedelta(0).as_unit(unit)
+        end = Timedelta(days=1).as_unit("s")
+
+        tdi = timedelta_range(start, end, freq="D")
+        assert tdi.unit == unit
+
+        tdi = timedelta_range(start, end.as_unit("ns"), freq="D")
+        assert tdi.unit == "ns"
+
+    def test_timedelta_range_unit_inference_tick(self):
+        start = Timedelta(0).as_unit("ms")
+        end = Timedelta(days=1).as_unit("s")
+
+        tdi = timedelta_range(start, end, freq="2000000us")
+        assert tdi.unit == "us"
+
+        tdi = timedelta_range(start, end.as_unit("ns"), freq="2000000us")
+        assert tdi.unit == "ns"