TST: add a test for core.missing._akima_interpolate pandas-dev#33426

pandas/tests/series/methods/test_interpolate.py

@@ -115,17 +115,29 @@ def test_interpolate_akima(self):
 
         ser = Series([10, 11, 12, 13])
 
+        # interpolate at new_index where `der` is zero
         expected = Series(
             [11.00, 11.25, 11.50, 11.75, 12.00, 12.25, 12.50, 12.75, 13.00],
             index=Index([1.0, 1.25, 1.5, 1.75, 2.0, 2.25, 2.5, 2.75, 3.0]),
         )
-        # interpolate at new_index
         new_index = ser.index.union(Index([1.25, 1.5, 1.75, 2.25, 2.5, 2.75])).astype(
             float
         )
         interp_s = ser.reindex(new_index).interpolate(method="akima")
         tm.assert_series_equal(interp_s[1:3], expected)
 
+        # interpolate at new_index where `der` is a non-zero int
+        expected = Series(
+            [11.0, 1.0, 1.0, 1.0, 12.0, 1.0, 1.0, 1.0, 13.0],
+            index=Index([1.0, 1.25, 1.5, 1.75, 2.0, 2.25, 2.5, 2.75, 3.0])
+        )
+        new_index = ser.index.union(Index([1.25, 1.5, 1.75, 2.25, 2.5, 2.75])).astype(
+            float
+        )
+        interp_s = ser.reindex(new_index).interpolate(method="akima", der=1)
+        tm.assert_series_equal(interp_s[1:3], expected)
+
+
     @td.skip_if_no_scipy
     def test_interpolate_piecewise_polynomial(self):
         ser = Series([10, 11, 12, 13])