diff --git a/pandas/core/arrays/datetimes.py b/pandas/core/arrays/datetimes.py
index 2c1ef7f05fa03..53d02e92946d9 100644
--- a/pandas/core/arrays/datetimes.py
+++ b/pandas/core/arrays/datetimes.py
@@ -1031,7 +1031,7 @@ def tz_localize(
 
         if self.tz is not None:
             if tz is None:
-                new_dates = tz_convert_from_utc(self.asi8, self.tz)
+                new_dates = tz_convert_from_utc(self.asi8, self.tz, reso=self._creso)
             else:
                 raise TypeError("Already tz-aware, use tz_convert to convert.")
         else:
diff --git a/pandas/core/resample.py b/pandas/core/resample.py
index d6cba824767b5..3c26299c93b70 100644
--- a/pandas/core/resample.py
+++ b/pandas/core/resample.py
@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import copy
-from datetime import timedelta
 from textwrap import dedent
 from typing import (
     TYPE_CHECKING,
@@ -90,7 +89,6 @@
 )
 from pandas.tseries.offsets import (
     Day,
-    Nano,
     Tick,
 )
 
@@ -1715,7 +1713,7 @@ def _get_time_bins(self, ax: DatetimeIndex):
             name=ax.name,
             ambiguous=True,
             nonexistent="shift_forward",
-        )
+        ).as_unit(ax.unit)
 
         ax_values = ax.asi8
         binner, bin_edges = self._adjust_bin_edges(binner, ax_values)
@@ -1751,7 +1749,11 @@ def _adjust_bin_edges(self, binner, ax_values):
             if self.closed == "right":
                 # GH 21459, GH 9119: Adjust the bins relative to the wall time
                 bin_edges = binner.tz_localize(None)
-                bin_edges = bin_edges + timedelta(1) - Nano(1)
+                bin_edges = (
+                    bin_edges
+                    + Timedelta(days=1, unit=bin_edges.unit).as_unit(bin_edges.unit)
+                    - Timedelta(1, unit=bin_edges.unit).as_unit(bin_edges.unit)
+                )
                 bin_edges = bin_edges.tz_localize(binner.tz).asi8
             else:
                 bin_edges = binner.asi8
diff --git a/pandas/tests/resample/test_datetime_index.py b/pandas/tests/resample/test_datetime_index.py
index 0c264c107d3d6..d5720f9628073 100644
--- a/pandas/tests/resample/test_datetime_index.py
+++ b/pandas/tests/resample/test_datetime_index.py
@@ -51,9 +51,14 @@ def _static_values(index):
     return np.random.rand(len(index))
 
 
-def test_custom_grouper(index):
+@pytest.fixture(params=["s", "ms", "us", "ns"])
+def unit(request):
+    return request.param
 
-    dti = index
+
+def test_custom_grouper(index, unit):
+
+    dti = index.as_unit(unit)
     s = Series(np.array([1] * len(dti)), index=dti, dtype="int64")
 
     b = Grouper(freq=Minute(5))
@@ -80,7 +85,7 @@ def test_custom_grouper(index):
     arr = [1] + [5] * 2592
     idx = dti[0:-1:5]
     idx = idx.append(dti[-1:])
-    idx = DatetimeIndex(idx, freq="5T")
+    idx = DatetimeIndex(idx, freq="5T").as_unit(unit)
     expect = Series(arr, index=idx)
 
     # GH2763 - return input dtype if we can
@@ -88,9 +93,9 @@ def test_custom_grouper(index):
     tm.assert_series_equal(result, expect)
 
 
-def test_custom_grouper_df(index):
+def test_custom_grouper_df(index, unit):
     b = Grouper(freq=Minute(5), closed="right", label="right")
-    dti = index
+    dti = index.as_unit(unit)
     df = DataFrame(np.random.rand(len(dti), 10), index=dti, dtype="float64")
     r = df.groupby(b).agg(np.sum)
 
@@ -123,22 +128,26 @@ def test_custom_grouper_df(index):
         ),
     ],
 )
-def test_resample_basic(series, closed, expected):
+def test_resample_basic(series, closed, expected, unit):
     s = series
+    s.index = s.index.as_unit(unit)
     expected = expected(s)
+    expected.index = expected.index.as_unit(unit)
     result = s.resample("5min", closed=closed, label="right").mean()
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_integerarray():
+def test_resample_integerarray(unit):
     # GH 25580, resample on IntegerArray
     ts = Series(
-        range(9), index=date_range("1/1/2000", periods=9, freq="T"), dtype="Int64"
+        range(9),
+        index=date_range("1/1/2000", periods=9, freq="T").as_unit(unit),
+        dtype="Int64",
     )
     result = ts.resample("3T").sum()
     expected = Series(
         [3, 12, 21],
-        index=date_range("1/1/2000", periods=3, freq="3T"),
+        index=date_range("1/1/2000", periods=3, freq="3T").as_unit(unit),
         dtype="Int64",
     )
     tm.assert_series_equal(result, expected)
@@ -146,14 +155,15 @@ def test_resample_integerarray():
     result = ts.resample("3T").mean()
     expected = Series(
         [1, 4, 7],
-        index=date_range("1/1/2000", periods=3, freq="3T"),
+        index=date_range("1/1/2000", periods=3, freq="3T").as_unit(unit),
         dtype="Float64",
     )
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_basic_grouper(series):
+def test_resample_basic_grouper(series, unit):
     s = series
+    s.index = s.index.as_unit(unit)
     result = s.resample("5Min").last()
     grouper = Grouper(freq=Minute(5), closed="left", label="left")
     expected = s.groupby(grouper).agg(lambda x: x[-1])
@@ -168,9 +178,10 @@ def test_resample_basic_grouper(series):
     "keyword,value",
     [("label", "righttt"), ("closed", "righttt"), ("convention", "starttt")],
 )
-def test_resample_string_kwargs(series, keyword, value):
+def test_resample_string_kwargs(series, keyword, value, unit):
     # see gh-19303
     # Check that wrong keyword argument strings raise an error
+    series.index = series.index.as_unit(unit)
     msg = f"Unsupported value {value} for `{keyword}`"
     with pytest.raises(ValueError, match=msg):
         series.resample("5min", **({keyword: value}))
@@ -180,18 +191,21 @@ def test_resample_string_kwargs(series, keyword, value):
     "_index_start,_index_end,_index_name",
     [("1/1/2000 00:00:00", "1/1/2000 00:13:00", "index")],
 )
-def test_resample_how(series, downsample_method):
+def test_resample_how(series, downsample_method, unit):
     if downsample_method == "ohlc":
         pytest.skip("covered by test_resample_how_ohlc")
 
     s = series
+    s.index = s.index.as_unit(unit)
     grouplist = np.ones_like(s)
     grouplist[0] = 0
     grouplist[1:6] = 1
     grouplist[6:11] = 2
     grouplist[11:] = 3
     expected = s.groupby(grouplist).agg(downsample_method)
-    expected.index = date_range("1/1/2000", periods=4, freq="5min", name="index")
+    expected.index = date_range(
+        "1/1/2000", periods=4, freq="5min", name="index"
+    ).as_unit(unit)
 
     result = getattr(
         s.resample("5min", closed="right", label="right"), downsample_method
@@ -203,8 +217,9 @@ def test_resample_how(series, downsample_method):
     "_index_start,_index_end,_index_name",
     [("1/1/2000 00:00:00", "1/1/2000 00:13:00", "index")],
 )
-def test_resample_how_ohlc(series):
+def test_resample_how_ohlc(series, unit):
     s = series
+    s.index = s.index.as_unit(unit)
     grouplist = np.ones_like(s)
     grouplist[0] = 0
     grouplist[1:6] = 1
@@ -218,7 +233,9 @@ def _ohlc(group):
 
     expected = DataFrame(
         s.groupby(grouplist).agg(_ohlc).values.tolist(),
-        index=date_range("1/1/2000", periods=4, freq="5min", name="index"),
+        index=date_range("1/1/2000", periods=4, freq="5min", name="index").as_unit(
+            unit
+        ),
         columns=["open", "high", "low", "close"],
     )
 
@@ -227,9 +244,11 @@ def _ohlc(group):
 
 
 @pytest.mark.parametrize("func", ["min", "max", "sum", "prod", "mean", "var", "std"])
-def test_numpy_compat(func):
+def test_numpy_compat(func, unit):
     # see gh-12811
-    s = Series([1, 2, 3, 4, 5], index=date_range("20130101", periods=5, freq="s"))
+    s = Series(
+        [1, 2, 3, 4, 5], index=date_range("20130101", periods=5, freq="s").as_unit(unit)
+    )
     r = s.resample("2s")
 
     msg = "numpy operations are not valid with resample"
@@ -240,10 +259,10 @@ def test_numpy_compat(func):
         getattr(r, func)(axis=1)
 
 
-def test_resample_how_callables():
+def test_resample_how_callables(unit):
     # GH#7929
     data = np.arange(5, dtype=np.int64)
-    ind = date_range(start="2014-01-01", periods=len(data), freq="d")
+    ind = date_range(start="2014-01-01", periods=len(data), freq="d").as_unit(unit)
     df = DataFrame({"A": data, "B": data}, index=ind)
 
     def fn(x, a=1):
@@ -265,7 +284,7 @@ def __call__(self, x):
     tm.assert_frame_equal(df_standard, df_class)
 
 
-def test_resample_rounding():
+def test_resample_rounding(unit):
     # GH 8371
     # odd results when rounding is needed
 
@@ -295,43 +314,49 @@ def test_resample_rounding():
         parse_dates={"timestamp": ["date", "time"]},
         index_col="timestamp",
     )
+    df.index = df.index.as_unit(unit)
     df.index.name = None
     result = df.resample("6s").sum()
     expected = DataFrame(
-        {"value": [4, 9, 4, 2]}, index=date_range("2014-11-08", freq="6s", periods=4)
+        {"value": [4, 9, 4, 2]},
+        index=date_range("2014-11-08", freq="6s", periods=4).as_unit(unit),
     )
     tm.assert_frame_equal(result, expected)
 
     result = df.resample("7s").sum()
     expected = DataFrame(
-        {"value": [4, 10, 4, 1]}, index=date_range("2014-11-08", freq="7s", periods=4)
+        {"value": [4, 10, 4, 1]},
+        index=date_range("2014-11-08", freq="7s", periods=4).as_unit(unit),
     )
     tm.assert_frame_equal(result, expected)
 
     result = df.resample("11s").sum()
     expected = DataFrame(
-        {"value": [11, 8]}, index=date_range("2014-11-08", freq="11s", periods=2)
+        {"value": [11, 8]},
+        index=date_range("2014-11-08", freq="11s", periods=2).as_unit(unit),
     )
     tm.assert_frame_equal(result, expected)
 
     result = df.resample("13s").sum()
     expected = DataFrame(
-        {"value": [13, 6]}, index=date_range("2014-11-08", freq="13s", periods=2)
+        {"value": [13, 6]},
+        index=date_range("2014-11-08", freq="13s", periods=2).as_unit(unit),
     )
     tm.assert_frame_equal(result, expected)
 
     result = df.resample("17s").sum()
     expected = DataFrame(
-        {"value": [16, 3]}, index=date_range("2014-11-08", freq="17s", periods=2)
+        {"value": [16, 3]},
+        index=date_range("2014-11-08", freq="17s", periods=2).as_unit(unit),
     )
     tm.assert_frame_equal(result, expected)
 
 
-def test_resample_basic_from_daily():
+def test_resample_basic_from_daily(unit):
     # from daily
     dti = date_range(
         start=datetime(2005, 1, 1), end=datetime(2005, 1, 10), freq="D", name="index"
-    )
+    ).as_unit(unit)
 
     s = Series(np.random.rand(len(dti)), dti)
 
@@ -385,10 +410,10 @@ def test_resample_basic_from_daily():
     assert result.index.name == "index"
 
 
-def test_resample_upsampling_picked_but_not_correct():
+def test_resample_upsampling_picked_but_not_correct(unit):
 
     # Test for issue #3020
-    dates = date_range("01-Jan-2014", "05-Jan-2014", freq="D")
+    dates = date_range("01-Jan-2014", "05-Jan-2014", freq="D").as_unit(unit)
     series = Series(1, index=dates)
 
     result = series.resample("D").mean()
@@ -401,8 +426,10 @@ def test_resample_upsampling_picked_but_not_correct():
     s = Series(
         np.arange(1.0, 6), index=[datetime(1975, 1, i, 12, 0) for i in range(1, 6)]
     )
+    s.index = s.index.as_unit(unit)
     expected = Series(
-        np.arange(1.0, 6), index=date_range("19750101", periods=5, freq="D")
+        np.arange(1.0, 6),
+        index=date_range("19750101", periods=5, freq="D").as_unit(unit),
     )
 
     result = s.resample("D").count()
@@ -415,8 +442,9 @@ def test_resample_upsampling_picked_but_not_correct():
 
 
 @pytest.mark.parametrize("f", ["sum", "mean", "prod", "min", "max", "var"])
-def test_resample_frame_basic_cy_funcs(f):
+def test_resample_frame_basic_cy_funcs(f, unit):
     df = tm.makeTimeDataFrame()
+    df.index = df.index.as_unit(unit)
 
     b = Grouper(freq="M")
     g = df.groupby(b)
@@ -426,23 +454,25 @@ def test_resample_frame_basic_cy_funcs(f):
 
 
 @pytest.mark.parametrize("freq", ["A", "M"])
-def test_resample_frame_basic_M_A(freq):
+def test_resample_frame_basic_M_A(freq, unit):
     df = tm.makeTimeDataFrame()
+    df.index = df.index.as_unit(unit)
     result = df.resample(freq).mean()
     tm.assert_series_equal(result["A"], df["A"].resample(freq).mean())
 
 
 @pytest.mark.parametrize("freq", ["W-WED", "M"])
-def test_resample_frame_basic_kind(freq):
+def test_resample_frame_basic_kind(freq, unit):
     df = tm.makeTimeDataFrame()
+    df.index = df.index.as_unit(unit)
     df.resample(freq, kind="period").mean()
 
 
-def test_resample_upsample():
+def test_resample_upsample(unit):
     # from daily
     dti = date_range(
         start=datetime(2005, 1, 1), end=datetime(2005, 1, 10), freq="D", name="index"
-    )
+    ).as_unit(unit)
 
     s = Series(np.random.rand(len(dti)), dti)
 
@@ -455,7 +485,7 @@ def test_resample_upsample():
     assert result.index.name == "index"
 
 
-def test_resample_how_method():
+def test_resample_how_method(unit):
     # GH9915
     s = Series(
         [11, 22],
@@ -464,6 +494,7 @@ def test_resample_how_method():
             Timestamp("2015-03-31 21:49:52.739000"),
         ],
     )
+    s.index = s.index.as_unit(unit)
     expected = Series(
         [11, np.NaN, np.NaN, np.NaN, np.NaN, np.NaN, 22],
         index=DatetimeIndex(
@@ -479,22 +510,23 @@ def test_resample_how_method():
             freq="10s",
         ),
     )
+    expected.index = expected.index.as_unit(unit)
     tm.assert_series_equal(s.resample("10S").mean(), expected)
 
 
-def test_resample_extra_index_point():
+def test_resample_extra_index_point(unit):
     # GH#9756
-    index = date_range(start="20150101", end="20150331", freq="BM")
+    index = date_range(start="20150101", end="20150331", freq="BM").as_unit(unit)
     expected = DataFrame({"A": Series([21, 41, 63], index=index)})
 
-    index = date_range(start="20150101", end="20150331", freq="B")
+    index = date_range(start="20150101", end="20150331", freq="B").as_unit(unit)
     df = DataFrame({"A": Series(range(len(index)), index=index)}, dtype="int64")
     result = df.resample("BM").last()
     tm.assert_frame_equal(result, expected)
 
 
-def test_upsample_with_limit():
-    rng = date_range("1/1/2000", periods=3, freq="5t")
+def test_upsample_with_limit(unit):
+    rng = date_range("1/1/2000", periods=3, freq="5t").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), rng)
 
     result = ts.resample("t").ffill(limit=2)
@@ -504,9 +536,11 @@ def test_upsample_with_limit():
 
 @pytest.mark.parametrize("freq", ["5D", "10H", "5Min", "10S"])
 @pytest.mark.parametrize("rule", ["Y", "3M", "15D", "30H", "15Min", "30S"])
-def test_nearest_upsample_with_limit(tz_aware_fixture, freq, rule):
+def test_nearest_upsample_with_limit(tz_aware_fixture, freq, rule, unit):
     # GH 33939
-    rng = date_range("1/1/2000", periods=3, freq=freq, tz=tz_aware_fixture)
+    rng = date_range("1/1/2000", periods=3, freq=freq, tz=tz_aware_fixture).as_unit(
+        unit
+    )
     ts = Series(np.random.randn(len(rng)), rng)
 
     result = ts.resample(rule).nearest(limit=2)
@@ -514,8 +548,9 @@ def test_nearest_upsample_with_limit(tz_aware_fixture, freq, rule):
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_ohlc(series):
+def test_resample_ohlc(series, unit):
     s = series
+    s.index = s.index.as_unit(unit)
 
     grouper = Grouper(freq=Minute(5))
     expect = s.groupby(grouper).agg(lambda x: x[-1])
@@ -537,11 +572,11 @@ def test_resample_ohlc(series):
     assert xs["close"] == s[4]
 
 
-def test_resample_ohlc_result():
+def test_resample_ohlc_result(unit):
 
     # GH 12332
-    index = date_range("1-1-2000", "2-15-2000", freq="h")
-    index = index.union(date_range("4-15-2000", "5-15-2000", freq="h"))
+    index = date_range("1-1-2000", "2-15-2000", freq="h").as_unit(unit)
+    index = index.union(date_range("4-15-2000", "5-15-2000", freq="h").as_unit(unit))
     s = Series(range(len(index)), index=index)
 
     a = s.loc[:"4-15-2000"].resample("30T").ohlc()
@@ -551,10 +586,10 @@ def test_resample_ohlc_result():
     assert isinstance(b, DataFrame)
 
 
-def test_resample_ohlc_result_odd_period():
+def test_resample_ohlc_result_odd_period(unit):
     # GH12348
     # raising on odd period
-    rng = date_range("2013-12-30", "2014-01-07")
+    rng = date_range("2013-12-30", "2014-01-07").as_unit(unit)
     index = rng.drop(
         [
             Timestamp("2014-01-01"),
@@ -565,11 +600,11 @@ def test_resample_ohlc_result_odd_period():
     )
     df = DataFrame(data=np.arange(len(index)), index=index)
     result = df.resample("B").mean()
-    expected = df.reindex(index=date_range(rng[0], rng[-1], freq="B"))
+    expected = df.reindex(index=date_range(rng[0], rng[-1], freq="B").as_unit(unit))
     tm.assert_frame_equal(result, expected)
 
 
-def test_resample_ohlc_dataframe():
+def test_resample_ohlc_dataframe(unit):
     df = (
         DataFrame(
             {
@@ -586,6 +621,7 @@ def test_resample_ohlc_dataframe():
             }
         )
     ).reindex(["VOLUME", "PRICE"], axis=1)
+    df.index = df.index.as_unit(unit)
     df.columns.name = "Cols"
     res = df.resample("H").ohlc()
     exp = pd.concat(
@@ -632,8 +668,10 @@ def test_resample_dup_index():
     tm.assert_frame_equal(result, expected)
 
 
-def test_resample_reresample():
-    dti = date_range(start=datetime(2005, 1, 1), end=datetime(2005, 1, 10), freq="D")
+def test_resample_reresample(unit):
+    dti = date_range(
+        start=datetime(2005, 1, 1), end=datetime(2005, 1, 10), freq="D"
+    ).as_unit(unit)
     s = Series(np.random.rand(len(dti)), dti)
     bs = s.resample("B", closed="right", label="right").mean()
     result = bs.resample("8H").mean()
@@ -650,8 +688,11 @@ def test_resample_reresample():
         ["M", {"start": "1990-01", "end": "2000-01", "freq": "M"}],
     ],
 )
-def test_resample_timestamp_to_period(simple_date_range_series, freq, expected_kwargs):
+def test_resample_timestamp_to_period(
+    simple_date_range_series, freq, expected_kwargs, unit
+):
     ts = simple_date_range_series("1/1/1990", "1/1/2000")
+    ts.index = ts.index.as_unit(unit)
 
     result = ts.resample(freq, kind="period").mean()
     expected = ts.resample(freq).mean()
@@ -659,13 +700,13 @@ def test_resample_timestamp_to_period(simple_date_range_series, freq, expected_k
     tm.assert_series_equal(result, expected)
 
 
-def test_ohlc_5min():
+def test_ohlc_5min(unit):
     def _ohlc(group):
         if isna(group).all():
             return np.repeat(np.nan, 4)
         return [group[0], group.max(), group.min(), group[-1]]
 
-    rng = date_range("1/1/2000 00:00:00", "1/1/2000 5:59:50", freq="10s")
+    rng = date_range("1/1/2000 00:00:00", "1/1/2000 5:59:50", freq="10s").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
     resampled = ts.resample("5min", closed="right", label="right").ohlc()
@@ -679,8 +720,8 @@ def _ohlc(group):
     assert (resampled.loc["1/1/2000 6:00:00"] == exp).all()
 
 
-def test_downsample_non_unique():
-    rng = date_range("1/1/2000", "2/29/2000")
+def test_downsample_non_unique(unit):
+    rng = date_range("1/1/2000", "2/29/2000").as_unit(unit)
     rng2 = rng.repeat(5).values
     ts = Series(np.random.randn(len(rng2)), index=rng2)
 
@@ -692,9 +733,9 @@ def test_downsample_non_unique():
     tm.assert_almost_equal(result[1], expected[2])
 
 
-def test_asfreq_non_unique():
+def test_asfreq_non_unique(unit):
     # GH #1077
-    rng = date_range("1/1/2000", "2/29/2000")
+    rng = date_range("1/1/2000", "2/29/2000").as_unit(unit)
     rng2 = rng.repeat(2).values
     ts = Series(np.random.randn(len(rng2)), index=rng2)
 
@@ -703,8 +744,8 @@ def test_asfreq_non_unique():
         ts.asfreq("B")
 
 
-def test_resample_axis1():
-    rng = date_range("1/1/2000", "2/29/2000")
+def test_resample_axis1(unit):
+    rng = date_range("1/1/2000", "2/29/2000").as_unit(unit)
     df = DataFrame(np.random.randn(3, len(rng)), columns=rng, index=["a", "b", "c"])
 
     result = df.resample("M", axis=1).mean()
@@ -713,13 +754,13 @@ def test_resample_axis1():
 
 
 @pytest.mark.parametrize("freq", ["t", "5t", "15t", "30t", "4h", "12h"])
-def test_resample_anchored_ticks(freq):
+def test_resample_anchored_ticks(freq, unit):
     # If a fixed delta (5 minute, 4 hour) evenly divides a day, we should
     # "anchor" the origin at midnight so we get regular intervals rather
     # than starting from the first timestamp which might start in the
     # middle of a desired interval
 
-    rng = date_range("1/1/2000 04:00:00", periods=86400, freq="s")
+    rng = date_range("1/1/2000 04:00:00", periods=86400, freq="s").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
     ts[:2] = np.nan  # so results are the same
     result = ts[2:].resample(freq, closed="left", label="left").mean()
@@ -728,33 +769,38 @@ def test_resample_anchored_ticks(freq):
 
 
 @pytest.mark.parametrize("end", [1, 2])
-def test_resample_single_group(end):
+def test_resample_single_group(end, unit):
     mysum = lambda x: x.sum()
 
-    rng = date_range("2000-1-1", f"2000-{end}-10", freq="D")
+    rng = date_range("2000-1-1", f"2000-{end}-10", freq="D").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
     tm.assert_series_equal(ts.resample("M").sum(), ts.resample("M").apply(mysum))
 
 
-def test_resample_single_group_std():
+def test_resample_single_group_std(unit):
     # GH 3849
     s = Series(
         [30.1, 31.6],
         index=[Timestamp("20070915 15:30:00"), Timestamp("20070915 15:40:00")],
     )
-    expected = Series([0.75], index=DatetimeIndex([Timestamp("20070915")], freq="D"))
+    s.index = s.index.as_unit(unit)
+    expected = Series(
+        [0.75], index=DatetimeIndex([Timestamp("20070915")], freq="D").as_unit(unit)
+    )
     result = s.resample("D").apply(lambda x: np.std(x))
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_offset():
+def test_resample_offset(unit):
     # GH 31809
 
-    rng = date_range("1/1/2000 00:00:00", "1/1/2000 02:00", freq="s")
+    rng = date_range("1/1/2000 00:00:00", "1/1/2000 02:00", freq="s").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
     resampled = ts.resample("5min", offset="2min").mean()
-    exp_rng = date_range("12/31/1999 23:57:00", "1/1/2000 01:57", freq="5min")
+    exp_rng = date_range("12/31/1999 23:57:00", "1/1/2000 01:57", freq="5min").as_unit(
+        unit
+    )
     tm.assert_index_equal(resampled.index, exp_rng)
 
 
@@ -769,12 +815,14 @@ def test_resample_offset():
         {"offset": "-3m"},
     ],
 )
-def test_resample_origin(kwargs):
+def test_resample_origin(kwargs, unit):
     # GH 31809
-    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s")
+    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
-    exp_rng = date_range("1999-12-31 23:57:00", "2000-01-01 01:57", freq="5min")
+    exp_rng = date_range(
+        "1999-12-31 23:57:00", "2000-01-01 01:57", freq="5min"
+    ).as_unit(unit)
 
     resampled = ts.resample("5min", **kwargs).mean()
     tm.assert_index_equal(resampled.index, exp_rng)
@@ -783,8 +831,8 @@ def test_resample_origin(kwargs):
 @pytest.mark.parametrize(
     "origin", ["invalid_value", "epch", "startday", "startt", "2000-30-30", object()]
 )
-def test_resample_bad_origin(origin):
-    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s")
+def test_resample_bad_origin(origin, unit):
+    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
     msg = (
         "'origin' should be equal to 'epoch', 'start', 'start_day', "
@@ -796,27 +844,31 @@ def test_resample_bad_origin(origin):
 
 
 @pytest.mark.parametrize("offset", ["invalid_value", "12dayys", "2000-30-30", object()])
-def test_resample_bad_offset(offset):
-    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s")
+def test_resample_bad_offset(offset, unit):
+    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
     msg = f"'offset' should be a Timedelta convertible type. Got '{offset}' instead."
     with pytest.raises(ValueError, match=msg):
         ts.resample("5min", offset=offset)
 
 
-def test_resample_origin_prime_freq():
+def test_resample_origin_prime_freq(unit):
     # GH 31809
     start, end = "2000-10-01 23:30:00", "2000-10-02 00:30:00"
-    rng = date_range(start, end, freq="7min")
+    rng = date_range(start, end, freq="7min").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
-    exp_rng = date_range("2000-10-01 23:14:00", "2000-10-02 00:22:00", freq="17min")
+    exp_rng = date_range(
+        "2000-10-01 23:14:00", "2000-10-02 00:22:00", freq="17min"
+    ).as_unit(unit)
     resampled = ts.resample("17min").mean()
     tm.assert_index_equal(resampled.index, exp_rng)
     resampled = ts.resample("17min", origin="start_day").mean()
     tm.assert_index_equal(resampled.index, exp_rng)
 
-    exp_rng = date_range("2000-10-01 23:30:00", "2000-10-02 00:21:00", freq="17min")
+    exp_rng = date_range(
+        "2000-10-01 23:30:00", "2000-10-02 00:21:00", freq="17min"
+    ).as_unit(unit)
     resampled = ts.resample("17min", origin="start").mean()
     tm.assert_index_equal(resampled.index, exp_rng)
     resampled = ts.resample("17min", offset="23h30min").mean()
@@ -824,24 +876,32 @@ def test_resample_origin_prime_freq():
     resampled = ts.resample("17min", origin="start_day", offset="23h30min").mean()
     tm.assert_index_equal(resampled.index, exp_rng)
 
-    exp_rng = date_range("2000-10-01 23:18:00", "2000-10-02 00:26:00", freq="17min")
+    exp_rng = date_range(
+        "2000-10-01 23:18:00", "2000-10-02 00:26:00", freq="17min"
+    ).as_unit(unit)
     resampled = ts.resample("17min", origin="epoch").mean()
     tm.assert_index_equal(resampled.index, exp_rng)
 
-    exp_rng = date_range("2000-10-01 23:24:00", "2000-10-02 00:15:00", freq="17min")
+    exp_rng = date_range(
+        "2000-10-01 23:24:00", "2000-10-02 00:15:00", freq="17min"
+    ).as_unit(unit)
     resampled = ts.resample("17min", origin="2000-01-01").mean()
     tm.assert_index_equal(resampled.index, exp_rng)
 
 
-def test_resample_origin_with_tz():
+def test_resample_origin_with_tz(unit):
     # GH 31809
     msg = "The origin must have the same timezone as the index."
 
     tz = "Europe/Paris"
-    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s", tz=tz)
+    rng = date_range(
+        "2000-01-01 00:00:00", "2000-01-01 02:00", freq="s", tz=tz
+    ).as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
-    exp_rng = date_range("1999-12-31 23:57:00", "2000-01-01 01:57", freq="5min", tz=tz)
+    exp_rng = date_range(
+        "1999-12-31 23:57:00", "2000-01-01 01:57", freq="5min", tz=tz
+    ).as_unit(unit)
     resampled = ts.resample("5min", origin="1999-12-31 23:57:00+00:00").mean()
     tm.assert_index_equal(resampled.index, exp_rng)
 
@@ -856,16 +916,16 @@ def test_resample_origin_with_tz():
         ts.resample("5min", origin="12/31/1999 23:57:00").mean()
 
     # if the series is not tz aware, origin should not be tz aware
-    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s")
+    rng = date_range("2000-01-01 00:00:00", "2000-01-01 02:00", freq="s").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
     with pytest.raises(ValueError, match=msg):
         ts.resample("5min", origin="12/31/1999 23:57:00+03:00").mean()
 
 
-def test_resample_origin_epoch_with_tz_day_vs_24h():
+def test_resample_origin_epoch_with_tz_day_vs_24h(unit):
     # GH 34474
     start, end = "2000-10-01 23:30:00+0500", "2000-12-02 00:30:00+0500"
-    rng = date_range(start, end, freq="7min")
+    rng = date_range(start, end, freq="7min").as_unit(unit)
     random_values = np.random.randn(len(rng))
     ts_1 = Series(random_values, index=rng)
 
@@ -882,7 +942,7 @@ def test_resample_origin_epoch_with_tz_day_vs_24h():
 
     # check that we have the similar results with two different timezones (+2H and +5H)
     start, end = "2000-10-01 23:30:00+0200", "2000-12-02 00:30:00+0200"
-    rng = date_range(start, end, freq="7min")
+    rng = date_range(start, end, freq="7min").as_unit(unit)
     ts_2 = Series(random_values, index=rng)
     result_5 = ts_2.resample("D", origin="epoch").mean()
     result_6 = ts_2.resample("24H", origin="epoch").mean()
@@ -890,7 +950,7 @@ def test_resample_origin_epoch_with_tz_day_vs_24h():
     tm.assert_series_equal(result_1.tz_localize(None), result_6.tz_localize(None))
 
 
-def test_resample_origin_with_day_freq_on_dst():
+def test_resample_origin_with_day_freq_on_dst(unit):
     # GH 31809
     tz = "America/Chicago"
 
@@ -899,13 +959,13 @@ def _create_series(values, timestamps, freq="D"):
             values,
             index=DatetimeIndex(
                 [Timestamp(t, tz=tz) for t in timestamps], freq=freq, ambiguous=True
-            ),
+            ).as_unit(unit),
         )
 
     # test classical behavior of origin in a DST context
     start = Timestamp("2013-11-02", tz=tz)
     end = Timestamp("2013-11-03 23:59", tz=tz)
-    rng = date_range(start, end, freq="1h")
+    rng = date_range(start, end, freq="1h").as_unit(unit)
     ts = Series(np.ones(len(rng)), index=rng)
 
     expected = _create_series([24.0, 25.0], ["2013-11-02", "2013-11-03"])
@@ -916,7 +976,7 @@ def _create_series(values, timestamps, freq="D"):
     # test complex behavior of origin/offset in a DST context
     start = Timestamp("2013-11-03", tz=tz)
     end = Timestamp("2013-11-03 23:59", tz=tz)
-    rng = date_range(start, end, freq="1h")
+    rng = date_range(start, end, freq="1h").as_unit(unit)
     ts = Series(np.ones(len(rng)), index=rng)
 
     expected_ts = ["2013-11-02 22:00-05:00", "2013-11-03 22:00-06:00"]
@@ -945,8 +1005,8 @@ def _create_series(values, timestamps, freq="D"):
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_daily_anchored():
-    rng = date_range("1/1/2000 0:00:00", periods=10000, freq="T")
+def test_resample_daily_anchored(unit):
+    rng = date_range("1/1/2000 0:00:00", periods=10000, freq="T").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
     ts[:2] = np.nan  # so results are the same
 
@@ -955,10 +1015,10 @@ def test_resample_daily_anchored():
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_to_period_monthly_buglet():
+def test_resample_to_period_monthly_buglet(unit):
     # GH #1259
 
-    rng = date_range("1/1/2000", "12/31/2000")
+    rng = date_range("1/1/2000", "12/31/2000").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
     result = ts.resample("M", kind="period").mean()
@@ -980,7 +1040,7 @@ def test_period_with_agg():
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_segfault():
+def test_resample_segfault(unit):
     # GH 8573
     # segfaulting in older versions
     all_wins_and_wagers = [
@@ -993,19 +1053,20 @@ def test_resample_segfault():
     df = DataFrame.from_records(
         all_wins_and_wagers, columns=("ID", "timestamp", "A", "B")
     ).set_index("timestamp")
+    df.index = df.index.as_unit(unit)
     result = df.groupby("ID").resample("5min").sum()
     expected = df.groupby("ID").apply(lambda x: x.resample("5min").sum())
     tm.assert_frame_equal(result, expected)
 
 
-def test_resample_dtype_preservation():
+def test_resample_dtype_preservation(unit):
 
     # GH 12202
     # validation tests for dtype preservation
 
     df = DataFrame(
         {
-            "date": date_range(start="2016-01-01", periods=4, freq="W"),
+            "date": date_range(start="2016-01-01", periods=4, freq="W").as_unit(unit),
             "group": [1, 1, 2, 2],
             "val": Series([5, 6, 7, 8], dtype="int32"),
         }
@@ -1018,13 +1079,13 @@ def test_resample_dtype_preservation():
     assert result.val.dtype == np.int32
 
 
-def test_resample_dtype_coercion():
+def test_resample_dtype_coercion(unit):
 
     pytest.importorskip("scipy.interpolate")
 
     # GH 16361
     df = {"a": [1, 3, 1, 4]}
-    df = DataFrame(df, index=date_range("2017-01-01", "2017-01-04"))
+    df = DataFrame(df, index=date_range("2017-01-01", "2017-01-04").as_unit(unit))
 
     expected = df.astype("float64").resample("H").mean()["a"].interpolate("cubic")
 
@@ -1035,9 +1096,9 @@ def test_resample_dtype_coercion():
     tm.assert_series_equal(result, expected)
 
 
-def test_weekly_resample_buglet():
+def test_weekly_resample_buglet(unit):
     # #1327
-    rng = date_range("1/1/2000", freq="B", periods=20)
+    rng = date_range("1/1/2000", freq="B", periods=20).as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
     resampled = ts.resample("W").mean()
@@ -1045,9 +1106,9 @@ def test_weekly_resample_buglet():
     tm.assert_series_equal(resampled, expected)
 
 
-def test_monthly_resample_error():
+def test_monthly_resample_error(unit):
     # #1451
-    dates = date_range("4/16/2012 20:00", periods=5000, freq="h")
+    dates = date_range("4/16/2012 20:00", periods=5000, freq="h").as_unit(unit)
     ts = Series(np.random.randn(len(dates)), index=dates)
     # it works!
     ts.resample("M")
@@ -1069,16 +1130,16 @@ def test_nanosecond_resample_error():
     tm.assert_series_equal(result, exp)
 
 
-def test_resample_anchored_intraday(simple_date_range_series):
+def test_resample_anchored_intraday(simple_date_range_series, unit):
     # #1471, #1458
 
-    rng = date_range("1/1/2012", "4/1/2012", freq="100min")
+    rng = date_range("1/1/2012", "4/1/2012", freq="100min").as_unit(unit)
     df = DataFrame(rng.month, index=rng)
 
     result = df.resample("M").mean()
     expected = df.resample("M", kind="period").mean().to_timestamp(how="end")
     expected.index += Timedelta(1, "ns") - Timedelta(1, "D")
-    expected.index = expected.index._with_freq("infer")
+    expected.index = expected.index.as_unit(unit)._with_freq("infer")
     assert expected.index.freq == "M"
     tm.assert_frame_equal(result, expected)
 
@@ -1087,11 +1148,11 @@ def test_resample_anchored_intraday(simple_date_range_series):
     exp = exp.to_timestamp(how="end")
 
     exp.index = exp.index + Timedelta(1, "ns") - Timedelta(1, "D")
-    exp.index = exp.index._with_freq("infer")
+    exp.index = exp.index.as_unit(unit)._with_freq("infer")
     assert exp.index.freq == "M"
     tm.assert_frame_equal(result, exp)
 
-    rng = date_range("1/1/2012", "4/1/2012", freq="100min")
+    rng = date_range("1/1/2012", "4/1/2012", freq="100min").as_unit(unit)
     df = DataFrame(rng.month, index=rng)
 
     result = df.resample("Q").mean()
@@ -1099,6 +1160,7 @@ def test_resample_anchored_intraday(simple_date_range_series):
     expected.index += Timedelta(1, "ns") - Timedelta(1, "D")
     expected.index._data.freq = "Q"
     expected.index._freq = lib.no_default
+    expected.index = expected.index.as_unit(unit)
     tm.assert_frame_equal(result, expected)
 
     result = df.resample("Q", closed="left").mean()
@@ -1107,16 +1169,19 @@ def test_resample_anchored_intraday(simple_date_range_series):
     expected.index += Timedelta(1, "ns") - Timedelta(1, "D")
     expected.index._data.freq = "Q"
     expected.index._freq = lib.no_default
+    expected.index = expected.index.as_unit(unit)
     tm.assert_frame_equal(result, expected)
 
     ts = simple_date_range_series("2012-04-29 23:00", "2012-04-30 5:00", freq="h")
+    ts.index = ts.index.as_unit(unit)
     resampled = ts.resample("M").mean()
     assert len(resampled) == 1
 
 
 @pytest.mark.parametrize("freq", ["MS", "BMS", "QS-MAR", "AS-DEC", "AS-JUN"])
-def test_resample_anchored_monthstart(simple_date_range_series, freq):
+def test_resample_anchored_monthstart(simple_date_range_series, freq, unit):
     ts = simple_date_range_series("1/1/2000", "12/31/2002")
+    ts.index = ts.index.as_unit(unit)
     ts.resample(freq).mean()
 
 
@@ -1139,14 +1204,14 @@ def test_resample_anchored_multiday(label, sec):
     assert result.index[-1] == Timestamp(f"2014-10-15 23:00:{sec}00")
 
 
-def test_corner_cases():
+def test_corner_cases(unit):
     # miscellaneous test coverage
 
-    rng = date_range("1/1/2000", periods=12, freq="t")
+    rng = date_range("1/1/2000", periods=12, freq="t").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
     result = ts.resample("5t", closed="right", label="left").mean()
-    ex_index = date_range("1999-12-31 23:55", periods=4, freq="5t")
+    ex_index = date_range("1999-12-31 23:55", periods=4, freq="5t").as_unit(unit)
     tm.assert_index_equal(result.index, ex_index)
 
 
@@ -1158,24 +1223,25 @@ def test_corner_cases_period(simple_period_range_series):
     assert len(result) == 0
 
 
-def test_corner_cases_date(simple_date_range_series):
+def test_corner_cases_date(simple_date_range_series, unit):
     # resample to periods
     ts = simple_date_range_series("2000-04-28", "2000-04-30 11:00", freq="h")
+    ts.index = ts.index.as_unit(unit)
     result = ts.resample("M", kind="period").mean()
     assert len(result) == 1
     assert result.index[0] == Period("2000-04", freq="M")
 
 
-def test_anchored_lowercase_buglet():
-    dates = date_range("4/16/2012 20:00", periods=50000, freq="s")
+def test_anchored_lowercase_buglet(unit):
+    dates = date_range("4/16/2012 20:00", periods=50000, freq="s").as_unit(unit)
     ts = Series(np.random.randn(len(dates)), index=dates)
     # it works!
     ts.resample("d").mean()
 
 
-def test_upsample_apply_functions():
+def test_upsample_apply_functions(unit):
     # #1596
-    rng = date_range("2012-06-12", periods=4, freq="h")
+    rng = date_range("2012-06-12", periods=4, freq="h").as_unit(unit)
 
     ts = Series(np.random.randn(len(rng)), index=rng)
 
@@ -1183,8 +1249,8 @@ def test_upsample_apply_functions():
     assert isinstance(result, DataFrame)
 
 
-def test_resample_not_monotonic():
-    rng = date_range("2012-06-12", periods=200, freq="h")
+def test_resample_not_monotonic(unit):
+    rng = date_range("2012-06-12", periods=200, freq="h").as_unit(unit)
     ts = Series(np.random.randn(len(rng)), index=rng)
 
     ts = ts.take(np.random.permutation(len(ts)))
@@ -1224,9 +1290,10 @@ def test_resample_median_bug_1688(dtype):
     tm.assert_frame_equal(result, exp)
 
 
-def test_how_lambda_functions(simple_date_range_series):
+def test_how_lambda_functions(simple_date_range_series, unit):
 
     ts = simple_date_range_series("1/1/2000", "4/1/2000")
+    ts.index = ts.index.as_unit(unit)
 
     result = ts.resample("M").apply(lambda x: x.mean())
     exp = ts.resample("M").mean()
@@ -1251,29 +1318,29 @@ def test_how_lambda_functions(simple_date_range_series):
     tm.assert_series_equal(result["bar"], bar_exp, check_names=False)
 
 
-def test_resample_unequal_times():
+def test_resample_unequal_times(unit):
     # #1772
     start = datetime(1999, 3, 1, 5)
     # end hour is less than start
     end = datetime(2012, 7, 31, 4)
-    bad_ind = date_range(start, end, freq="30min")
+    bad_ind = date_range(start, end, freq="30min").as_unit(unit)
     df = DataFrame({"close": 1}, index=bad_ind)
 
     # it works!
     df.resample("AS").sum()
 
 
-def test_resample_consistency():
+def test_resample_consistency(unit):
 
     # GH 6418
     # resample with bfill / limit / reindex consistency
 
-    i30 = date_range("2002-02-02", periods=4, freq="30T")
+    i30 = date_range("2002-02-02", periods=4, freq="30T").as_unit(unit)
     s = Series(np.arange(4.0), index=i30)
     s[2] = np.NaN
 
     # Upsample by factor 3 with reindex() and resample() methods:
-    i10 = date_range(i30[0], i30[-1], freq="10T")
+    i10 = date_range(i30[0], i30[-1], freq="10T").as_unit(unit)
 
     s10 = s.reindex(index=i10, method="bfill")
     s10_2 = s.reindex(index=i10, method="bfill", limit=2)
@@ -1335,7 +1402,7 @@ def test_resample_timegrouper(dates):
     tm.assert_frame_equal(result, expected)
 
 
-def test_resample_nunique():
+def test_resample_nunique(unit):
 
     # GH 12352
     df = DataFrame(
@@ -1350,6 +1417,7 @@ def test_resample_nunique():
             },
         }
     )
+    df.index = df.index.as_unit(unit)
     r = df.resample("D")
     g = df.groupby(Grouper(freq="D"))
     expected = df.groupby(Grouper(freq="D")).ID.apply(lambda x: x.nunique())
@@ -1366,9 +1434,10 @@ def test_resample_nunique():
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_nunique_preserves_column_level_names():
+def test_resample_nunique_preserves_column_level_names(unit):
     # see gh-23222
     df = tm.makeTimeDataFrame(freq="1D").abs()
+    df.index = df.index.as_unit(unit)
     df.columns = pd.MultiIndex.from_arrays(
         [df.columns.tolist()] * 2, names=["lev0", "lev1"]
     )
@@ -1385,11 +1454,11 @@ def test_resample_nunique_preserves_column_level_names():
     ],
     ids=["nunique", "series_nunique", "nunique_str"],
 )
-def test_resample_nunique_with_date_gap(func):
+def test_resample_nunique_with_date_gap(func, unit):
     # GH 13453
     # Since all elements are unique, these should all be the same
-    index = date_range("1-1-2000", "2-15-2000", freq="h")
-    index2 = date_range("4-15-2000", "5-15-2000", freq="h")
+    index = date_range("1-1-2000", "2-15-2000", freq="h").as_unit(unit)
+    index2 = date_range("4-15-2000", "5-15-2000", freq="h").as_unit(unit)
     index3 = index.append(index2)
     s = Series(range(len(index3)), index=index3, dtype="int64")
     r = s.resample("M")
@@ -1400,17 +1469,17 @@ def test_resample_nunique_with_date_gap(func):
 
 @pytest.mark.parametrize("n", [10000, 100000])
 @pytest.mark.parametrize("k", [10, 100, 1000])
-def test_resample_group_info(n, k):
+def test_resample_group_info(n, k, unit):
     # GH10914
 
     # use a fixed seed to always have the same uniques
     prng = np.random.RandomState(1234)
 
-    dr = date_range(start="2015-08-27", periods=n // 10, freq="T")
+    dr = date_range(start="2015-08-27", periods=n // 10, freq="T").as_unit(unit)
     ts = Series(prng.randint(0, n // k, n).astype("int64"), index=prng.choice(dr, n))
 
     left = ts.resample("30T").nunique()
-    ix = date_range(start=ts.index.min(), end=ts.index.max(), freq="30T")
+    ix = date_range(start=ts.index.min(), end=ts.index.max(), freq="30T").as_unit(unit)
 
     vals = ts.values
     bins = np.searchsorted(ix.values, ts.index, side="right")
@@ -1427,13 +1496,13 @@ def test_resample_group_info(n, k):
     tm.assert_series_equal(left, right)
 
 
-def test_resample_size():
+def test_resample_size(unit):
     n = 10000
-    dr = date_range("2015-09-19", periods=n, freq="T")
+    dr = date_range("2015-09-19", periods=n, freq="T").as_unit(unit)
     ts = Series(np.random.randn(n), index=np.random.choice(dr, n))
 
     left = ts.resample("7T").size()
-    ix = date_range(start=left.index.min(), end=ts.index.max(), freq="7T")
+    ix = date_range(start=left.index.min(), end=ts.index.max(), freq="7T").as_unit(unit)
 
     bins = np.searchsorted(ix.values, ts.index.values, side="right")
     val = np.bincount(bins, minlength=len(ix) + 1)[1:].astype("int64", copy=False)
@@ -1474,29 +1543,31 @@ def test_resample_across_dst():
     tm.assert_frame_equal(result, expected)
 
 
-def test_groupby_with_dst_time_change():
+def test_groupby_with_dst_time_change(unit):
     # GH 24972
-    index = DatetimeIndex(
-        [1478064900001000000, 1480037118776792000], tz="UTC"
-    ).tz_convert("America/Chicago")
+    index = (
+        DatetimeIndex([1478064900001000000, 1480037118776792000], tz="UTC")
+        .tz_convert("America/Chicago")
+        .as_unit(unit)
+    )
 
     df = DataFrame([1, 2], index=index)
     result = df.groupby(Grouper(freq="1d")).last()
     expected_index_values = date_range(
         "2016-11-02", "2016-11-24", freq="d", tz="America/Chicago"
-    )
+    ).as_unit(unit)
 
     index = DatetimeIndex(expected_index_values)
     expected = DataFrame([1.0] + ([np.nan] * 21) + [2.0], index=index)
     tm.assert_frame_equal(result, expected)
 
 
-def test_resample_dst_anchor():
+def test_resample_dst_anchor(unit):
     # 5172
-    dti = DatetimeIndex([datetime(2012, 11, 4, 23)], tz="US/Eastern")
+    dti = DatetimeIndex([datetime(2012, 11, 4, 23)], tz="US/Eastern").as_unit(unit)
     df = DataFrame([5], index=dti)
 
-    dti = DatetimeIndex(df.index.normalize(), freq="D")
+    dti = DatetimeIndex(df.index.normalize(), freq="D").as_unit(unit)
     expected = DataFrame([5], index=dti)
     tm.assert_frame_equal(df.resample(rule="D").sum(), expected)
     df.resample(rule="MS").sum()
@@ -1504,11 +1575,15 @@ def test_resample_dst_anchor():
         df.resample(rule="MS").sum(),
         DataFrame(
             [5],
-            index=DatetimeIndex([datetime(2012, 11, 1)], tz="US/Eastern", freq="MS"),
+            index=DatetimeIndex(
+                [datetime(2012, 11, 1)], tz="US/Eastern", freq="MS"
+            ).as_unit(unit),
         ),
     )
 
-    dti = date_range("2013-09-30", "2013-11-02", freq="30Min", tz="Europe/Paris")
+    dti = date_range(
+        "2013-09-30", "2013-11-02", freq="30Min", tz="Europe/Paris"
+    ).as_unit(unit)
     values = range(dti.size)
     df = DataFrame({"a": values, "b": values, "c": values}, index=dti, dtype="int64")
     how = {"a": "min", "b": "max", "c": "count"}
@@ -1521,7 +1596,9 @@ def test_resample_dst_anchor():
                 "b": [47, 383, 719, 1055, 1393, 1586],
                 "c": [48, 336, 336, 336, 338, 193],
             },
-            index=date_range("9/30/2013", "11/4/2013", freq="W-MON", tz="Europe/Paris"),
+            index=date_range(
+                "9/30/2013", "11/4/2013", freq="W-MON", tz="Europe/Paris"
+            ).as_unit(unit),
         ),
         "W-MON Frequency",
     )
@@ -1536,7 +1613,7 @@ def test_resample_dst_anchor():
             },
             index=date_range(
                 "9/30/2013", "11/11/2013", freq="2W-MON", tz="Europe/Paris"
-            ),
+            ).as_unit(unit),
         ),
         "2W-MON Frequency",
     )
@@ -1545,7 +1622,9 @@ def test_resample_dst_anchor():
         df.resample("MS").agg(how)[["a", "b", "c"]],
         DataFrame(
             {"a": [0, 48, 1538], "b": [47, 1537, 1586], "c": [48, 1490, 49]},
-            index=date_range("9/1/2013", "11/1/2013", freq="MS", tz="Europe/Paris"),
+            index=date_range(
+                "9/1/2013", "11/1/2013", freq="MS", tz="Europe/Paris"
+            ).as_unit(unit),
         ),
         "MS Frequency",
     )
@@ -1554,7 +1633,9 @@ def test_resample_dst_anchor():
         df.resample("2MS").agg(how)[["a", "b", "c"]],
         DataFrame(
             {"a": [0, 1538], "b": [1537, 1586], "c": [1538, 49]},
-            index=date_range("9/1/2013", "11/1/2013", freq="2MS", tz="Europe/Paris"),
+            index=date_range(
+                "9/1/2013", "11/1/2013", freq="2MS", tz="Europe/Paris"
+            ).as_unit(unit),
         ),
         "2MS Frequency",
     )
@@ -1570,32 +1651,34 @@ def test_resample_dst_anchor():
                 "b": [1295, 1345, 1393, 1441],
                 "c": [48, 50, 48, 48],
             },
-            index=date_range("10/26/2013", "10/29/2013", freq="D", tz="Europe/Paris"),
+            index=date_range(
+                "10/26/2013", "10/29/2013", freq="D", tz="Europe/Paris"
+            ).as_unit(unit),
         ),
         "D Frequency",
     )
 
 
-def test_downsample_across_dst():
+def test_downsample_across_dst(unit):
     # GH 8531
     tz = pytz.timezone("Europe/Berlin")
     dt = datetime(2014, 10, 26)
-    dates = date_range(tz.localize(dt), periods=4, freq="2H")
+    dates = date_range(tz.localize(dt), periods=4, freq="2H").as_unit(unit)
     result = Series(5, index=dates).resample("H").mean()
     expected = Series(
         [5.0, np.nan] * 3 + [5.0],
-        index=date_range(tz.localize(dt), periods=7, freq="H"),
+        index=date_range(tz.localize(dt), periods=7, freq="H").as_unit(unit),
     )
     tm.assert_series_equal(result, expected)
 
 
-def test_downsample_across_dst_weekly():
+def test_downsample_across_dst_weekly(unit):
     # GH 9119, GH 21459
     df = DataFrame(
         index=DatetimeIndex(
             ["2017-03-25", "2017-03-26", "2017-03-27", "2017-03-28", "2017-03-29"],
             tz="Europe/Amsterdam",
-        ),
+        ).as_unit(unit),
         data=[11, 12, 13, 14, 15],
     )
     result = df.resample("1W").sum()
@@ -1603,28 +1686,32 @@ def test_downsample_across_dst_weekly():
         [23, 42],
         index=DatetimeIndex(
             ["2017-03-26", "2017-04-02"], tz="Europe/Amsterdam", freq="W"
-        ),
+        ).as_unit(unit),
     )
     tm.assert_frame_equal(result, expected)
 
 
-def test_downsample_across_dst_weekly_2():
+def test_downsample_across_dst_weekly_2(unit):
     # GH 9119, GH 21459
-    idx = date_range("2013-04-01", "2013-05-01", tz="Europe/London", freq="H")
+    idx = date_range("2013-04-01", "2013-05-01", tz="Europe/London", freq="H").as_unit(
+        unit
+    )
     s = Series(index=idx, dtype=np.float64)
     result = s.resample("W").mean()
     expected = Series(
-        index=date_range("2013-04-07", freq="W", periods=5, tz="Europe/London"),
+        index=date_range("2013-04-07", freq="W", periods=5, tz="Europe/London").as_unit(
+            unit
+        ),
         dtype=np.float64,
     )
     tm.assert_series_equal(result, expected)
 
 
-def test_downsample_dst_at_midnight():
+def test_downsample_dst_at_midnight(unit):
     # GH 25758
     start = datetime(2018, 11, 3, 12)
     end = datetime(2018, 11, 5, 12)
-    index = date_range(start, end, freq="1H")
+    index = date_range(start, end, freq="1H").as_unit(unit)
     index = index.tz_localize("UTC").tz_convert("America/Havana")
     data = list(range(len(index)))
     dataframe = DataFrame(data, index=index)
@@ -1633,12 +1720,12 @@ def test_downsample_dst_at_midnight():
     dti = date_range("2018-11-03", periods=3).tz_localize(
         "America/Havana", ambiguous=True
     )
-    dti = DatetimeIndex(dti, freq="D")
+    dti = DatetimeIndex(dti, freq="D").as_unit(unit)
     expected = DataFrame([7.5, 28.0, 44.5], index=dti)
     tm.assert_frame_equal(result, expected)
 
 
-def test_resample_with_nat():
+def test_resample_with_nat(unit):
     # GH 13020
     index = DatetimeIndex(
         [
@@ -1650,35 +1737,39 @@ def test_resample_with_nat():
         ]
     )
     frame = DataFrame([2, 3, 5, 7, 11], index=index)
+    frame.index = frame.index.as_unit(unit)
 
     index_1s = DatetimeIndex(
         ["1970-01-01 00:00:00", "1970-01-01 00:00:01", "1970-01-01 00:00:02"]
-    )
+    ).as_unit(unit)
     frame_1s = DataFrame([3.0, 7.0, 11.0], index=index_1s)
     tm.assert_frame_equal(frame.resample("1s").mean(), frame_1s)
 
-    index_2s = DatetimeIndex(["1970-01-01 00:00:00", "1970-01-01 00:00:02"])
+    index_2s = DatetimeIndex(["1970-01-01 00:00:00", "1970-01-01 00:00:02"]).as_unit(
+        unit
+    )
     frame_2s = DataFrame([5.0, 11.0], index=index_2s)
     tm.assert_frame_equal(frame.resample("2s").mean(), frame_2s)
 
-    index_3s = DatetimeIndex(["1970-01-01 00:00:00"])
+    index_3s = DatetimeIndex(["1970-01-01 00:00:00"]).as_unit(unit)
     frame_3s = DataFrame([7.0], index=index_3s)
     tm.assert_frame_equal(frame.resample("3s").mean(), frame_3s)
 
     tm.assert_frame_equal(frame.resample("60s").mean(), frame_3s)
 
 
-def test_resample_datetime_values():
+def test_resample_datetime_values(unit):
     # GH 13119
     # check that datetime dtype is preserved when NaT values are
     # introduced by the resampling
 
     dates = [datetime(2016, 1, 15), datetime(2016, 1, 19)]
     df = DataFrame({"timestamp": dates}, index=dates)
+    df.index = df.index.as_unit(unit)
 
     exp = Series(
         [datetime(2016, 1, 15), pd.NaT, datetime(2016, 1, 19)],
-        index=date_range("2016-01-15", periods=3, freq="2D"),
+        index=date_range("2016-01-15", periods=3, freq="2D").as_unit(unit),
         name="timestamp",
     )
 
@@ -1688,11 +1779,13 @@ def test_resample_datetime_values():
     tm.assert_series_equal(res, exp)
 
 
-def test_resample_apply_with_additional_args(series):
+def test_resample_apply_with_additional_args(series, unit):
     # GH 14615
     def f(data, add_arg):
         return np.mean(data) * add_arg
 
+    series.index = series.index.as_unit(unit)
+
     multiplier = 10
     result = series.resample("D").apply(f, multiplier)
     expected = series.resample("D").mean().multiply(multiplier)
@@ -1726,11 +1819,14 @@ def f(data, add_arg):
         (24, "H", 1, "D"),
     ],
 )
-def test_resample_equivalent_offsets(n1, freq1, n2, freq2, k):
+def test_resample_equivalent_offsets(n1, freq1, n2, freq2, k, unit):
     # GH 24127
     n1_ = n1 * k
     n2_ = n2 * k
-    s = Series(0, index=date_range("19910905 13:00", "19911005 07:00", freq=freq1))
+    s = Series(
+        0,
+        index=date_range("19910905 13:00", "19911005 07:00", freq=freq1).as_unit(unit),
+    )
     s = s + range(len(s))
 
     result1 = s.resample(str(n1_) + freq1).mean()
@@ -1749,11 +1845,11 @@ def test_resample_equivalent_offsets(n1, freq1, n2, freq2, k):
         ("1991-08", "1992-04", "M", "19910831", "19920531"),
     ],
 )
-def test_get_timestamp_range_edges(first, last, freq, exp_first, exp_last):
+def test_get_timestamp_range_edges(first, last, freq, exp_first, exp_last, unit):
     first = Period(first)
-    first = first.to_timestamp(first.freq)
+    first = first.to_timestamp(first.freq).as_unit(unit)
     last = Period(last)
-    last = last.to_timestamp(last.freq)
+    last = last.to_timestamp(last.freq).as_unit(unit)
 
     exp_first = Timestamp(exp_first)
     exp_last = Timestamp(exp_last)
@@ -1765,9 +1861,9 @@ def test_get_timestamp_range_edges(first, last, freq, exp_first, exp_last):
 
 
 @pytest.mark.parametrize("duplicates", [True, False])
-def test_resample_apply_product(duplicates):
+def test_resample_apply_product(duplicates, unit):
     # GH 5586
-    index = date_range(start="2012-01-31", freq="M", periods=12)
+    index = date_range(start="2012-01-31", freq="M", periods=12).as_unit(unit)
 
     ts = Series(range(12), index=index)
     df = DataFrame({"A": ts, "B": ts + 2})
@@ -1779,7 +1875,7 @@ def test_resample_apply_product(duplicates):
         np.array([[0, 24], [60, 210], [336, 720], [990, 1716]], dtype=np.int64),
         index=DatetimeIndex(
             ["2012-03-31", "2012-06-30", "2012-09-30", "2012-12-31"], freq="Q-DEC"
-        ),
+        ).as_unit(unit),
         columns=df.columns,
     )
     tm.assert_frame_equal(result, expected)
@@ -1821,34 +1917,39 @@ def test_resample_apply_product(duplicates):
     ],
 )
 def test_resample_calendar_day_with_dst(
-    first: str, last: str, freq_in: str, freq_out: str, exp_last: str
+    first: str, last: str, freq_in: str, freq_out: str, exp_last: str, unit
 ):
     # GH 35219
-    ts = Series(1.0, date_range(first, last, freq=freq_in, tz="Europe/Amsterdam"))
+    ts = Series(
+        1.0, date_range(first, last, freq=freq_in, tz="Europe/Amsterdam").as_unit(unit)
+    )
     result = ts.resample(freq_out).ffill()
     expected = Series(
-        1.0, date_range(first, exp_last, freq=freq_out, tz="Europe/Amsterdam")
+        1.0,
+        date_range(first, exp_last, freq=freq_out, tz="Europe/Amsterdam").as_unit(unit),
     )
     tm.assert_series_equal(result, expected)
 
 
 @pytest.mark.parametrize("func", ["min", "max", "first", "last"])
-def test_resample_aggregate_functions_min_count(func):
+def test_resample_aggregate_functions_min_count(func, unit):
     # GH#37768
-    index = date_range(start="2020", freq="M", periods=3)
+    index = date_range(start="2020", freq="M", periods=3).as_unit(unit)
     ser = Series([1, np.nan, np.nan], index)
     result = getattr(ser.resample("Q"), func)(min_count=2)
     expected = Series(
         [np.nan],
-        index=DatetimeIndex(["2020-03-31"], dtype="datetime64[ns]", freq="Q-DEC"),
+        index=DatetimeIndex(["2020-03-31"], freq="Q-DEC").as_unit(unit),
     )
     tm.assert_series_equal(result, expected)
 
 
-def test_resample_unsigned_int(any_unsigned_int_numpy_dtype):
+def test_resample_unsigned_int(any_unsigned_int_numpy_dtype, unit):
     # gh-43329
     df = DataFrame(
-        index=date_range(start="2000-01-01", end="2000-01-03 23", freq="12H"),
+        index=date_range(start="2000-01-01", end="2000-01-03 23", freq="12H").as_unit(
+            unit
+        ),
         columns=["x"],
         data=[0, 1, 0] * 2,
         dtype=any_unsigned_int_numpy_dtype,
@@ -1860,6 +1961,8 @@ def test_resample_unsigned_int(any_unsigned_int_numpy_dtype):
     expected = DataFrame(
         [1, np.nan, 0],
         columns=["x"],
-        index=date_range(start="2000-01-01", end="2000-01-03 23", freq="D"),
+        index=date_range(start="2000-01-01", end="2000-01-03 23", freq="D").as_unit(
+            unit
+        ),
     )
     tm.assert_frame_equal(result, expected)