Merge remote-tracking branch 'upstream/master' into fix_interpolate_l…

…imit_area_and_limit_direction_with_pad

Manually resolved conflicts:
 * doc/source/whatsnew/v1.1.0.rst: Just a conflicting line
 * pandas/tests/series/test_missing.py: All test for interpolation have
   been moved to a new file pandas/tests/series/methods/test_interpolate.py
   I accepted all changes from upstream, which removed my tests from
   test_missing.py and manually added my test to the new file
   methods/test_interpolate.py

doc/source/whatsnew/v1.1.0.rst

@@ -307,8 +307,8 @@ Indexing
 Missing
 ^^^^^^^
 
--  Bug in :meth:`Series.interpolate` where kwarg ``limit_area`` and ``limit_direction`` had no effect when using methods ``pad`` and `backfill`` (:issue:`31048`)
--
+- Calling :meth:`fillna` on an empty Series now correctly returns a shallow copied object. The behaviour is now consistent with :class:`Index`, :class:`DataFrame` and a non-empty :class:`Series` (:issue:`32543`).
+- Bug in :meth:`Series.interpolate` where kwarg ``limit_area`` and ``limit_direction`` had no effect when using methods ``pad`` and `backfill`` (:issue:`31048`)
 
 MultiIndex
 ^^^^^^^^^^

pandas/tests/series/methods/test_interpolate.py

@@ -400,6 +400,75 @@ def test_interp_limit_area(self):
         with pytest.raises(ValueError, match=msg):
             s.interpolate(method="linear", limit_area="abc")
 
+    def test_interp_limit_area_with_pad(self):
+        # Test for issue #26796
+        s = Series([np.nan, np.nan, 3, np.nan, np.nan, np.nan, 7, np.nan, np.nan])
+
+        expected = Series([np.nan, np.nan, 3.0, 3.0, 3.0, 3.0, 7.0, np.nan, np.nan])
+        result = s.interpolate(method="pad", limit_area="inside")
+        tm.assert_series_equal(result, expected)
+
+        expected = Series(
+            [np.nan, np.nan, 3.0, 3.0, np.nan, np.nan, 7.0, np.nan, np.nan]
+        )
+        result = s.interpolate(method="pad", limit_area="inside", limit=1)
+        tm.assert_series_equal(result, expected)
+
+        expected = Series([np.nan, np.nan, 3.0, np.nan, np.nan, np.nan, 7.0, 7.0, 7.0])
+        result = s.interpolate(method="pad", limit_area="outside")
+        tm.assert_series_equal(result, expected)
+
+        expected = Series(
+            [np.nan, np.nan, 3.0, np.nan, np.nan, np.nan, 7.0, 7.0, np.nan]
+        )
+        result = s.interpolate(method="pad", limit_area="outside", limit=1)
+        tm.assert_series_equal(result, expected)
+
+    def test_interp_limit_area_with_backfill(self):
+        # Test for issue #26796
+        s = Series([np.nan, np.nan, 3, np.nan, np.nan, np.nan, 7, np.nan, np.nan])
+
+        expected = Series([np.nan, np.nan, 3.0, 7.0, 7.0, 7.0, 7.0, np.nan, np.nan])
+        result = s.interpolate(method="bfill", limit_area="inside")
+        tm.assert_series_equal(result, expected)
+
+        expected = Series(
+            [np.nan, np.nan, 3.0, np.nan, np.nan, 7.0, 7.0, np.nan, np.nan]
+        )
+        result = s.interpolate(method="bfill", limit_area="inside", limit=1)
+        tm.assert_series_equal(result, expected)
+
+        expected = Series([3.0, 3.0, 3.0, np.nan, np.nan, np.nan, 7.0, np.nan, np.nan])
+        result = s.interpolate(method="bfill", limit_area="outside")
+        tm.assert_series_equal(result, expected)
+
+        expected = Series(
+            [np.nan, 3.0, 3.0, np.nan, np.nan, np.nan, 7.0, np.nan, np.nan]
+        )
+        result = s.interpolate(method="bfill", limit_area="outside", limit=1)
+        tm.assert_series_equal(result, expected)
+
+    def test_interp_raise_limit_direction_and_pad_or_bfill(self):
+        s = Series([1, 2, 3])
+        forbidden_combinations = [
+            ("pad", "backward"),
+            ("ffill", "backward"),
+            ("backfill", "forward"),
+            ("bfill", "forward"),
+            ("pad", "both"),
+            ("ffill", "both"),
+            ("backfill", "both"),
+            ("bfill", "both"),
+        ]
+
+        for method, limit_direction in forbidden_combinations:
+            msg = (
+                f"`limit_direction` must not be `{limit_direction}` "
+                f"for method `{method}`"
+            )
+            with pytest.raises(ValueError, match=msg):
+                s.interpolate(method=method, limit_direction=limit_direction)
+
     def test_interp_limit_direction(self):
         # These tests are for issue #9218 -- fill NaNs in both directions.
         s = Series([1, 3, np.nan, np.nan, np.nan, 11])