chore: clarify delist-filter exception

freqtrade/plugins/pairlist/DelistFilter.py

@@ -23,9 +23,10 @@ class DelistFilter(IPairList):
         self._max_days_from_now = self._pairlistconfig.get("max_days_from_now", 0)
         if self._max_days_from_now < 0:
             raise ConfigurationError("DelistFilter requires max_days_from_now to be >= 0")
-        if not self._exchange._ft_has["has_delisting"]:
+        if not self._exchange.get_option("has_delisting"):
             raise ConfigurationError(
-                "DelistFilter doesn't support this exchange and trading mode combination.",
+                f"DelistFilter doesn't support {self._exchange.name} in "
+                f"{self._exchange.trading_mode} mode."
             )
 
     def short_desc(self) -> str:

tests/plugins/test_pairlist.py

@@ -2850,10 +2850,10 @@ def test_backtesting_modes(
 def test_DelistFilter_error(whitelist_conf) -> None:
     whitelist_conf["pairlists"] = [{"method": "StaticPairList"}, {"method": "DelistFilter"}]
     exchange_mock = MagicMock()
-    exchange_mock._ft_has = {"has_delisting": False}
+    exchange_mock.get_option = MagicMock(return_value=False)
     with pytest.raises(
         OperationalException,
-        match=r"DelistFilter doesn't support this exchange and trading mode combination\.",
+        match=r"DelistFilter doesn't support .* in .* mode\.",
     ):
         PairListManager(exchange_mock, whitelist_conf, MagicMock())