minor refactor of tests

Author: minggli

pandas/tests/io/json/test_compression.py

@@ -21,7 +21,7 @@ def test_compression_roundtrip(compression):
         assert_frame_equal(df, pd.read_json(result))
 
 
-def test_to_csv_compression_size(compression):
+def test_to_json_compression_size(compression):
 
     df = pd.concat(100 * [pd.DataFrame([[0.123456, 0.234567, 0.567567],
                                         [12.32112, 123123.2, 321321.2]],

pandas/tests/io/test_pickle.py

@@ -464,7 +464,6 @@ def test_compression_size(self, compression):
                                            columns=['X', 'Y', 'Z'])])
 
         with tm.ensure_clean() as filename:
-            import os
             df.to_pickle(filename, compression=compression)
             file_size = os.path.getsize(filename)
 

pandas/tests/series/test_io.py

@@ -167,11 +167,11 @@ def test_to_csv_compression_size(self, compression):
 
         with ensure_clean() as filename:
             import os
-            s.to_csv(filename, compression=compression)
+            s.to_csv(filename, compression=compression, header=True)
             file_size = os.path.getsize(filename)
 
             if compression:
-                s.to_csv(filename, compression=None)
+                s.to_csv(filename, compression=None, header=True)
                 uncompressed_file_size = os.path.getsize(filename)
                 assert uncompressed_file_size > file_size