Update backtesting test

Had bad behavior before, and didn't properly test what it was supposed to

tests/optimize/test_backtesting.py

@@ -788,13 +788,14 @@ def test_backtest_one(default_conf, fee, mocker, testdatadir) -> None:
         assert len(t['orders']) == 2
         ln = data_pair.loc[data_pair["date"] == t["open_date"]]
         # Check open trade rate alignes to open rate
-        assert ln is not None
+        assert not ln.empty
         assert round(ln.iloc[0]["open"], 6) == round(t["open_rate"], 6)
         # check close trade rate alignes to close rate or is between high and low
-        ln = data_pair.loc[data_pair["date"] == t["close_date"]]
-        assert (round(ln.iloc[0]["open"], 6) == round(t["close_rate"], 6) or
-                round(ln.iloc[0]["low"], 6) < round(
-                t["close_rate"], 6) < round(ln.iloc[0]["high"], 6))
+        ln1 = data_pair.loc[data_pair["date"] == t["close_date"]]
+        assert not ln1.empty
+        assert (round(ln1.iloc[0]["open"], 6) == round(t["close_rate"], 6) or
+                round(ln1.iloc[0]["low"], 6) < round(
+                t["close_rate"], 6) < round(ln1.iloc[0]["high"], 6))
 
 
 def test_backtest_timedout_entry_orders(default_conf, fee, mocker, testdatadir) -> None: