add compression size test case

pandas/tests/io/json/test_compression.py

@@ -21,6 +21,24 @@ def test_compression_roundtrip(compression):
         assert_frame_equal(df, pd.read_json(result))
 
 
+def test_to_csv_compression_size(compression):
+
+    df = pd.concat(100 * [pd.DataFrame([[0.123456, 0.234567, 0.567567],
+                                        [12.32112, 123123.2, 321321.2]],
+                                       columns=['X', 'Y', 'Z'])],
+                   ignore_index=True)
+
+    with tm.ensure_clean() as filename:
+        import os
+        df.to_json(filename, compression=compression)
+        file_size = os.path.getsize(filename)
+
+        if compression:
+            df.to_json(filename, compression=None)
+            uncompressed_file_size = os.path.getsize(filename)
+            assert uncompressed_file_size > file_size
+
+
 def test_read_zipped_json():
     uncompressed_path = tm.get_data_path("tsframe_v012.json")
     uncompressed_df = pd.read_json(uncompressed_path)