TST/DOC applied TomAugspurger's feedback

* Added test for new test util `convert_rows_list_to_csv_str`
* Edited what's new

Related Issue: pandas-dev#20353

Author: deflatSOCO

doc/source/whatsnew/v0.24.0.txt

@@ -187,8 +187,7 @@ Other Enhancements
 
 Backwards incompatible API changes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- When file path is given by string format in :func:`DataFrame.to_csv`, it disables universal newline support.
-  - Instead, default value of `line_terminator` in :func:`DataFrame.to_csv` has changed from `'\n'` to `os.linesep`(:issue:`20353`)
+- :func:`DataFrame.to_csv` now uses :func:`os.linesep` rather than ``'\n'`` for the default line terminator.(:issue:`20353`)
 
 
 .. _whatsnew_0240.api_breaking.interval_values:

pandas/tests/io/formats/test_to_csv.py

@@ -360,7 +360,6 @@ def test_to_csv_string_with_lf(self):
                 b'2,"d\nef"' + os_linesep +
                 b'3,"g\nh\n\ni"' + os_linesep
             )
-
             df.to_csv(path, index=False)
             with open(path, 'rb') as f:
                 assert f.read() == expected_noarg
@@ -373,7 +372,6 @@ def test_to_csv_string_with_lf(self):
                 b'2,"d\nef"\n'
                 b'3,"g\nh\n\ni"\n'
             )
-
             df.to_csv(path, line_terminator='\n', index=False)
             with open(path, 'rb') as f:
                 assert f.read() == expected_lf
@@ -387,7 +385,6 @@ def test_to_csv_string_with_lf(self):
                 b'2,"d\nef"\r\n'
                 b'3,"g\nh\n\ni"\r\n'
             )
-
             df.to_csv(path, line_terminator='\r\n', index=False)
             with open(path, 'rb') as f:
                 assert f.read() == expected_crlf
@@ -409,7 +406,6 @@ def test_to_csv_string_with_crlf(self):
                 b'2,"d\r\nef"' + os_linesep +
                 b'3,"g\r\nh\r\n\r\ni"' + os_linesep
             )
-
             df.to_csv(path, index=False)
             with open(path, 'rb') as f:
                 assert f.read() == expected_noarg
@@ -422,7 +418,6 @@ def test_to_csv_string_with_crlf(self):
                 b'2,"d\r\nef"\n'
                 b'3,"g\r\nh\r\n\r\ni"\n'
             )
-
             df.to_csv(path, line_terminator='\n', index=False)
             with open(path, 'rb') as f:
                 assert f.read() == expected_lf
@@ -436,7 +431,6 @@ def test_to_csv_string_with_crlf(self):
                 b'2,"d\r\nef"\r\n'
                 b'3,"g\r\nh\r\n\r\ni"\r\n'
             )
-
             df.to_csv(path, line_terminator='\r\n', index=False)
             with open(path, 'rb') as f:
                 assert f.read() == expected_crlf

pandas/tests/util/test_testing.py

@@ -12,6 +12,7 @@
                                  assert_index_equal, assert_series_equal,
                                  assert_frame_equal, assert_numpy_array_equal,
                                  RNGContext)
+from pandas import compat
 
 
 class TestAssertAlmostEqual(object):
@@ -164,6 +165,15 @@ def test_raise_with_traceback(self):
                 _, _, traceback = sys.exc_info()
                 raise_with_traceback(e, traceback)
 
+    def test_convert_rows_list_to_csv_str(self):
+        rows_list = ["aaa", "bbb", "ccc"]
+        ret = tm.convert_rows_list_to_csv_str(rows_list)
+        if(compat.is_platform_windows()):
+            expected = "aaa\r\nbbb\r\nccc\r\n"
+        else:
+            expected = "aaa\nbbb\nccc\n"
+        assert ret == expected
+
 
 class TestAssertNumpyArrayEqual(object):