Don't fail if strategy doesn't contain sell signal

tests/strategy/test_interface.py

@@ -126,6 +126,27 @@ def test_get_signal_old_dataframe(default_conf, mocker, caplog, ohlcv_history):
     assert log_has('Outdated history for pair xyz. Last tick is 16 minutes old', caplog)
 
 
+def test_get_signal_no_sell_column(default_conf, mocker, caplog, ohlcv_history):
+    # default_conf defines a 5m interval. we check interval * 2 + 5m
+    # this is necessary as the last candle is removed (partial candles) by default
+    ohlcv_history.loc[1, 'date'] = arrow.utcnow()
+    # Take a copy to correctly modify the call
+    mocked_history = ohlcv_history.copy()
+    # Intentionally don't set sell column
+    # mocked_history['sell'] = 0
+    mocked_history['buy'] = 0
+    mocked_history.loc[1, 'buy'] = 1
+
+    caplog.set_level(logging.INFO)
+    mocker.patch.object(_STRATEGY, 'assert_df')
+
+    assert (True, False, None) == _STRATEGY.get_signal(
+        'xyz',
+        default_conf['timeframe'],
+        mocked_history
+    )
+
+
 def test_ignore_expired_candle(default_conf):
     default_conf.update({'strategy': 'DefaultStrategy'})
     strategy = StrategyResolver.load_strategy(default_conf)
@@ -197,10 +218,6 @@ def test_assert_df(ohlcv_history, caplog):
                        match="Buy column not set"):
         _STRATEGY.assert_df(ohlcv_history.drop('buy', axis=1), len(ohlcv_history),
                             ohlcv_history.loc[df_len, 'close'], ohlcv_history.loc[0, 'date'])
-    with pytest.raises(StrategyError,
-                       match="Sell column not set"):
-        _STRATEGY.assert_df(ohlcv_history.drop('sell', axis=1), len(ohlcv_history),
-                            ohlcv_history.loc[df_len, 'close'], ohlcv_history.loc[0, 'date'])
 
     _STRATEGY.disable_dataframe_checks = True
     caplog.clear()