update tests

Author: jbrockmendel

pandas/core/dtypes/cast.py

@@ -1191,7 +1191,7 @@ def maybe_infer_to_datetimelike(
         #  numpy would have done it for us.
         convert_numeric=False,
         convert_non_numeric=True,
-        dtype_if_all_nat=np.dtype("M8[ns]"),
+        dtype_if_all_nat=np.dtype("M8[s]"),
     )
 
 

pandas/tests/indexes/datetimes/test_date_range.py

@@ -185,6 +185,7 @@ def test_date_range_edges(self, freq):
             [ts + n * td for n in range(1, 5)],
             dtype="M8[ns]",
             freq=freq,
+            dtype="M8[ns]",
         )
         tm.assert_index_equal(idx, exp)
 

pandas/tests/indexes/test_base.py

@@ -177,7 +177,7 @@ def test_constructor_int_dtype_nan(self):
         "klass,dtype,na_val",
         [
             (Index, np.float64, np.nan),
-            (DatetimeIndex, "datetime64[ns]", pd.NaT),
+            (DatetimeIndex, "datetime64[s]", pd.NaT),
         ],
     )
     def test_index_ctor_infer_nan_nat(self, klass, dtype, na_val):

pandas/tests/indexes/test_index_new.py

@@ -141,6 +141,9 @@ def test_constructor_infer_nat_dt_like(
             )
 
         expected = klass([NaT, NaT])
+        if dtype[0] == "d":
+            # we infer all-NaT as second resolution
+            expected = expected.astype("M8[ns]")
         assert expected.dtype == dtype
         data = [ctor]
         data.insert(pos, nulls_fixture)

pandas/tests/tools/test_to_datetime.py

@@ -1568,7 +1568,7 @@ def test_to_datetime_cache_scalar(self):
             (
                 (None, np.nan) + (NaT,) * start_caching_at,
                 (NaT,) * (start_caching_at + 2),
-                "ns",
+                "s",
             ),
             (
                 (None, Timestamp("2012-07-26")) + (NaT,) * start_caching_at,
@@ -1618,7 +1618,7 @@ def test_convert_object_to_datetime_with_cache(
     )
     def test_to_datetime_converts_null_like_to_nat(self, cache, input):
         # GH35888
-        expected = Series([NaT] * len(input), dtype="M8[ns]")
+        expected = Series([NaT] * len(input), dtype="M8[s]")
         result = to_datetime(input, cache=cache)
         tm.assert_series_equal(result, expected)
 
@@ -3186,7 +3186,7 @@ def test_na_values_with_cache(
         self, cache, unique_nulls_fixture, unique_nulls_fixture2
     ):
         # GH22305
-        expected = Index([NaT, NaT], dtype="datetime64[ns]")
+        expected = Index([NaT, NaT], dtype="datetime64[s]")
         result = to_datetime([unique_nulls_fixture, unique_nulls_fixture2], cache=cache)
         tm.assert_index_equal(result, expected)