TST: Removed regex warning for read_csv

Follow-up to #13481 and partially fixes #13932.  Regex mistakenly
matches to the empty string, which will cause Python 3.x to issue a
warning.  In addition, not sure why this test was placed in
`python_parsers_only.py`...

Author: gfyoung <gfyoung17@gmail.com>

Closes #13943 from gfyoung/regex-empty-match and squashes the following commits:

b93325e [gfyoung] TST: Removed regex warning for read_csv

Author: gfyoung

pandas/io/tests/parser/common.py

@@ -1568,3 +1568,17 @@ def _encode_data_with_bom(_data):
                             encoding=utf8, names=['a'],
                             skip_blank_lines=False)
         tm.assert_frame_equal(out, expected)
+
+    def test_temporary_file(self):
+        # see gh-13398
+        data1 = "0 0"
+
+        from tempfile import TemporaryFile
+        new_file = TemporaryFile("w+")
+        new_file.write(data1)
+        new_file.flush()
+        new_file.seek(0)
+
+        result = self.read_csv(new_file, sep='\s+', header=None)
+        expected = DataFrame([[0, 0]])
+        tm.assert_frame_equal(result, expected)

pandas/io/tests/parser/python_parser_only.py

@@ -172,20 +172,6 @@ def test_read_table_buglet_4x_multiindex(self):
         actual = self.read_table(StringIO(data), sep='\s+')
         tm.assert_frame_equal(actual, expected)
 
-    def test_temporary_file(self):
-        # GH13398
-        data1 = "0 0"
-
-        from tempfile import TemporaryFile
-        new_file = TemporaryFile("w+")
-        new_file.write(data1)
-        new_file.flush()
-        new_file.seek(0)
-
-        result = self.read_csv(new_file, sep=r"\s*", header=None)
-        expected = DataFrame([[0, 0]])
-        tm.assert_frame_equal(result, expected)
-
     def test_skipfooter_with_decimal(self):
         # see gh-6971
         data = '1#2\n3#4'