Improve ShufflePairlist to shuffle only once per candle

tests/plugins/test_pairlist.py

@@ -2,6 +2,8 @@
 
 import logging
 import time
+from copy import deepcopy
+from datetime import timedelta
 from unittest.mock import MagicMock, PropertyMock
 
 import pandas as pd
@@ -719,15 +721,26 @@ def test_PerformanceFilter_error(mocker, whitelist_conf, caplog) -> None:
 def test_ShuffleFilter_init(mocker, whitelist_conf, caplog) -> None:
     whitelist_conf['pairlists'] = [
         {"method": "StaticPairList"},
-        {"method": "ShuffleFilter", "seed": 42}
+        {"method": "ShuffleFilter", "seed": 43}
     ]
 
     exchange = get_patched_exchange(mocker, whitelist_conf)
-    PairListManager(exchange, whitelist_conf)
-    assert log_has("Backtesting mode detected, applying seed value: 42", caplog)
+    plm = PairListManager(exchange, whitelist_conf)
+    assert log_has("Backtesting mode detected, applying seed value: 43", caplog)
+
+    with time_machine.travel("2021-09-01 05:01:00 +00:00") as t:
+        plm.refresh_pairlist()
+        pl1 = deepcopy(plm.whitelist)
+        plm.refresh_pairlist()
+        assert plm.whitelist == pl1
+
+        t.shift(timedelta(minutes=10))
+        plm.refresh_pairlist()
+        assert plm.whitelist != pl1
+
     caplog.clear()
     whitelist_conf['runmode'] = RunMode.DRY_RUN
-    PairListManager(exchange, whitelist_conf)
+    plm = PairListManager(exchange, whitelist_conf)
     assert not log_has("Backtesting mode detected, applying seed value: 42", caplog)
     assert log_has("Live mode detected, not applying seed.", caplog)