make requested changes

Author: rushabh-v

doc/source/whatsnew/v1.1.0.rst

@@ -168,7 +168,7 @@ MultiIndex
 I/O
 ^^^
 - Bug in :meth:`read_json` where integer overflow was occuring when json contains big number strings. (:issue:`30320`)
-- `read_csv` will now raise a ``ValueError`` when arguments `header` and `prefix` both are not None. (:issue:`27394`)
+- `read_csv` will now raise a ``ValueError`` when the arguments `header` and `prefix` both are not `None`. (:issue:`27394`)
 -
 
 Plotting

pandas/tests/io/parser/test_common.py

@@ -2044,7 +2044,9 @@ def test_read_csv_raises_on_header_prefix(all_parsers):
     # gh-27394
     parser = all_parsers
     msg = "Argument prefix must be None if argument header is not None"
+
     s = StringIO("0,1\n2,3")
+
     with pytest.raises(ValueError, match=msg):
         parser.read_csv(s, header=0, prefix="_X")