Unit tests for sandbox pass / fail scenarios

Big Wave of appreciation to xmatthias for the guidence on how
Mocker works

freqtrade/tests/exchange/test_exchange.py

@@ -63,24 +63,33 @@ def test_set_sandbox(default_conf, mocker):
     type(api_mock).urls = url_mock
     mocker.patch('freqtrade.exchange.Exchange._init_ccxt', MagicMock(return_value=api_mock))
     mocker.patch('freqtrade.exchange.Exchange.validate_timeframes', MagicMock())
-    Exchange(default_conf)
 
-# def test_set_sandbox_exception(default_conf, mocker):
-#     """
-#     Test Fail scenario
-#     """
-#     api_mock = MagicMock()
-#     api_mock.load_markets = MagicMock(return_value={
-#         'ETH/BTC': '', 'LTC/BTC': '', 'XRP/BTC': '', 'NEO/BTC': ''
-#     })
-#     url_mock = PropertyMock(return_value={'api': 'https://api.gdax.com'})
-#     type(api_mock).urls = url_mock
-#
-#     mocker.patch('freqtrade.exchange.Exchange._init_ccxt', MagicMock(return_value=api_mock))
-#     mocker.patch('freqtrade.exchange.Exchange.validate_timeframes', MagicMock())
-#
-#     with pytest.raises(OperationalException, match=r'does not provide a sandbox api'):
-#         Exchange(default_conf)
+    exchange = Exchange(default_conf)
+    liveurl = exchange._api.urls['api']
+    default_conf['exchange']['sandbox'] = True
+    exchange.set_sandbox(exchange._api, default_conf['exchange'], 'Logname')
+    assert exchange._api.urls['api'] != liveurl
+
+def test_set_sandbox_exception(default_conf, mocker):
+    """
+    Test Fail scenario
+    """
+    api_mock = MagicMock()
+    api_mock.load_markets = MagicMock(return_value={
+        'ETH/BTC': '', 'LTC/BTC': '', 'XRP/BTC': '', 'NEO/BTC': ''
+    })
+    url_mock = PropertyMock(return_value={'api': 'https://api.gdax.com'})
+    type(api_mock).urls = url_mock
+
+    mocker.patch('freqtrade.exchange.Exchange._init_ccxt', MagicMock(return_value=api_mock))
+    mocker.patch('freqtrade.exchange.Exchange.validate_timeframes', MagicMock())
+
+    with pytest.raises(OperationalException, match=r'does not provide a sandbox api'):
+        exchange = Exchange(default_conf)
+        default_conf['exchange']['sandbox'] = True
+        exchange.set_sandbox(exchange._api, default_conf['exchange'], 'Logname')
+        assert exchange._api.urls.get('test') == False
+
 
 def test_validate_pairs(default_conf, mocker):
     api_mock = MagicMock()