Fix missing import and adjust test to match GitHub description

Author: kinow

pandas/core/internals/blocks.py

@@ -7,7 +7,7 @@
 
 import numpy as np
 
-from pandas._libs import NaT, Timestamp, lib, tslib
+from pandas._libs import NaT, Timestamp, lib, tslib, writers
 import pandas._libs.internals as libinternals
 from pandas._libs.tslibs import Timedelta, conversion
 from pandas._libs.tslibs.timezones import tz_compare

pandas/tests/io/formats/test_to_csv.py

@@ -556,10 +556,11 @@ def test_to_csv_zip_arguments(self, compression, archive_name):
             archived_file = os.path.basename(zp.filelist[0].filename)
             assert archived_file == expected_arcname
 
-    @pytest.mark.parametrize("df_new_type", ["int64"])
+    @pytest.mark.parametrize("df_new_type", ["Int64"])
     def test_to_csv_na_rep_long_string(self, df_new_type):
         # see gh-25099
-        df = pd.DataFrame([np.nan] * 3, columns=['c'], dtype=df_new_type)
+        df = pd.DataFrame({"c": [float('nan')]*3})
+        df = df.astype(df_new_type)
         expected_rows = ['c',
                          'mynull',
                          'mynull',