BUG: record warnings related to DatetimeIndex (#37193)

pandas/tests/plotting/test_datetimelike.py

@@ -291,9 +291,16 @@ def test_irreg_hf(self):
         _, ax = self.plt.subplots()
         df2 = df.copy()
         df2.index = df.index.astype(object)
-        df2.plot(ax=ax)
-        diffs = Series(ax.get_lines()[0].get_xydata()[:, 0]).diff()
-        assert (np.fabs(diffs[1:] - sec) < 1e-8).all()
+        with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
+            # This warning will be emitted
+            # pandas/core/frame.py:3216:
+            # FutureWarning: Automatically casting object-dtype Index of datetimes
+            # to DatetimeIndex is deprecated and will be removed in a future version.
+            # Explicitly cast to DatetimeIndex instead.
+            # return klass(values, index=self.index, name=name, fastpath=True)
+            df2.plot(ax=ax)
+            diffs = Series(ax.get_lines()[0].get_xydata()[:, 0]).diff()
+            assert (np.fabs(diffs[1:] - sec) < 1e-8).all()
 
     def test_irregular_datetime64_repr_bug(self):
         ser = tm.makeTimeSeries()
@@ -1028,9 +1035,16 @@ def test_irreg_dtypes(self):
         # np.datetime64
         idx = date_range("1/1/2000", periods=10)
         idx = idx[[0, 2, 5, 9]].astype(object)
-        df = DataFrame(np.random.randn(len(idx), 3), idx)
-        _, ax = self.plt.subplots()
-        _check_plot_works(df.plot, ax=ax)
+        with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
+            # This warning will be emitted
+            # pandas/core/frame.py:3216:
+            # FutureWarning: Automatically casting object-dtype Index of datetimes
+            # to DatetimeIndex is deprecated and will be removed in a future version.
+            # Explicitly cast to DatetimeIndex instead.
+            # return klass(values, index=self.index, name=name, fastpath=True)
+            df = DataFrame(np.random.randn(len(idx), 3), idx)
+            _, ax = self.plt.subplots()
+            _check_plot_works(df.plot, ax=ax)
 
     @pytest.mark.slow
     def test_time(self):