diff --git a/freqtrade/misc.py b/freqtrade/misc.py
index afc4334e8..00d431723 100644
--- a/freqtrade/misc.py
+++ b/freqtrade/misc.py
@@ -14,6 +14,11 @@ from freqtrade import __version__
 logger = logging.getLogger(__name__)
 
 
+def file_dump_json(filename, data):
+    with open(filename, 'w') as fp:
+        json.dump(data, fp)
+
+
 class State(enum.Enum):
     RUNNING = 0
     STOPPED = 1
diff --git a/freqtrade/optimize/__init__.py b/freqtrade/optimize/__init__.py
index 2d73c3215..613bb7b17 100644
--- a/freqtrade/optimize/__init__.py
+++ b/freqtrade/optimize/__init__.py
@@ -8,6 +8,7 @@ from pandas import DataFrame
 from freqtrade.exchange import get_ticker_history
 from freqtrade.optimize.hyperopt_conf import hyperopt_optimize_conf
 from freqtrade.analyze import populate_indicators, parse_ticker_dataframe
+from freqtrade import misc
 
 logger = logging.getLogger(__name__)
 
@@ -127,7 +128,6 @@ def download_backtesting_testdata(datadir: str, pair: str, interval: int = 5) ->
     logger.debug("New End: {}".format(data[-1:][0]['T']))
     data = sorted(data, key=lambda data: data['T'])
 
-    with open(filename, "wt") as fp:
-        json.dump(data, fp)
+    misc.file_dump_json(filename, data)
 
     return True
diff --git a/freqtrade/tests/test_misc.py b/freqtrade/tests/test_misc.py
index 0b85000cb..e0cd70709 100644
--- a/freqtrade/tests/test_misc.py
+++ b/freqtrade/tests/test_misc.py
@@ -5,10 +5,11 @@ import argparse
 from copy import deepcopy
 
 import pytest
+from unittest.mock import MagicMock
 from jsonschema import ValidationError
 
 from freqtrade.misc import throttle, parse_args, load_config,\
-     parse_args_common
+     parse_args_common, file_dump_json
 
 
 def test_throttle():
@@ -135,6 +136,14 @@ def test_parse_args_hyperopt_custom(mocker):
     assert call_args.func is not None
 
 
+def test_file_dump_json(default_conf, mocker):
+    file_open = mocker.patch('freqtrade.misc.open', MagicMock())
+    json_dump = mocker.patch('json.dump', MagicMock())
+    file_dump_json('somefile', [1, 2, 3])
+    assert file_open.call_count == 1
+    assert json_dump.call_count == 1
+
+
 def test_load_config(default_conf, mocker):
     file_mock = mocker.patch('freqtrade.misc.open', mocker.mock_open(
         read_data=json.dumps(default_conf)
diff --git a/freqtrade/tests/testdata/download_backtest_data.py b/freqtrade/tests/testdata/download_backtest_data.py
index 37cd4c95f..32c36073b 100755
--- a/freqtrade/tests/testdata/download_backtest_data.py
+++ b/freqtrade/tests/testdata/download_backtest_data.py
@@ -1,11 +1,11 @@
 #!/usr/bin/env python3
 
 """This script generate json data from bittrex"""
-import json
 from os import path
 
 from freqtrade import exchange
 from freqtrade.exchange import Bittrex
+from freqtrade import misc
 
 PAIRS = [
     'BTC_BCC', 'BTC_ETH', 'BTC_MER', 'BTC_POWR', 'BTC_ETC',
@@ -25,5 +25,4 @@ for pair in PAIRS:
         pair,
         TICKER_INTERVAL,
     ))
-    with open(filename, 'w') as fp:
-        json.dump(data, fp)
+    misc.file_dump_json(filename, data)