Add whatnews and to_string decimal test

Author: thoo

doc/source/whatsnew/v0.24.0.txt

@@ -20,7 +20,8 @@ New features
 the user to override the engine's default behavior to include or omit the
 dataframe's indexes from the resulting Parquet file. (:issue:`20768`)
 - :meth:`DataFrame.corr` and :meth:`Series.corr` now accept a callable for generic calculation methods of correlation, e.g. histogram intersection (:issue:`22684`)
-
+- :func:`DataFrame.to_string` now accepts ``decimal`` as an argument, allowing
+the user to use a decimal separator. (:issue:`23614`)
 
 .. _whatsnew_0240.enhancements.extension_array_operators:
 
@@ -945,6 +946,7 @@ Other API Changes
 - :class:`DateOffset` attribute `_cacheable` and method `_should_cache` have been removed (:issue:`23118`)
 - Comparing :class:`Timedelta` to be less or greater than unknown types now raises a ``TypeError`` instead of returning ``False`` (:issue:`20829`)
 - :meth:`Index.hasnans` and :meth:`Series.hasnans` now always return a python boolean. Previously, a python or a numpy boolean could be returned, depending on circumstances (:issue:`23294`).
+- The order of the arguments of `DataFrame.to_html` and `DataFrame.to_string` is rearranged.
 
 .. _whatsnew_0240.deprecations:
 

pandas/tests/io/formats/test_format.py

@@ -1451,6 +1451,11 @@ def test_to_string_format_na(self):
                     '4  4.0     bar')
         assert result == expected
 
+    def test_to_string_decimal(self):
+        df = DataFrame({'A': [6.0, 3.1, 2.2]})
+        expected = '     A\n0  6,0\n1  3,1\n2  2,2'
+        assert df.to_string(decimal=',') == expected
+
     def test_to_string_line_width(self):
         df = DataFrame(123, lrange(10, 15), lrange(30))
         s = df.to_string(line_width=80)