Add test for informative pair filtering

tests/data/test_dataprovider.py

@@ -129,9 +129,14 @@ def test_get_pair_dataframe(mocker, default_conf, ohlcv_history, candle_type):
     default_conf["runmode"] = RunMode.BACKTEST
     dp = DataProvider(default_conf, exchange)
     assert dp.runmode == RunMode.BACKTEST
-    assert isinstance(dp.get_pair_dataframe(
-        "UNITTEST/BTC", timeframe, candle_type=candle_type), DataFrame)
-    # assert dp.get_pair_dataframe("NONESENSE/AAA", timeframe).empty
+    df = dp.get_pair_dataframe("UNITTEST/BTC", timeframe, candle_type=candle_type)
+    assert isinstance(df, DataFrame)
+    assert len(df) == 3  # ohlcv_history mock has just 3 rows
+
+    dp._set_dataframe_max_date(ohlcv_history.iloc[-1]['date'])
+    df = dp.get_pair_dataframe("UNITTEST/BTC", timeframe, candle_type=candle_type)
+    assert isinstance(df, DataFrame)
+    assert len(df) == 2  # ohlcv_history is limited to 2 rows now
 
 
 def test_available_pairs(mocker, default_conf, ohlcv_history):