test: improve test for ohlcv_with_cache

tests/exchange/test_exchange.py

@@ -2813,6 +2813,7 @@ def test_refresh_ohlcv_with_cache(mocker, default_conf, time_machine) -> None:
     ohlcv_mock.reset_mock()
     res = exchange.refresh_ohlcv_with_cache(pairs, start.timestamp())
     assert ohlcv_mock.call_count == 0
+    assert len(res) == 5
 
     # Expire 5m cache
     time_machine.move_to(start + timedelta(minutes=6), tick=False)
@@ -2821,6 +2822,7 @@ def test_refresh_ohlcv_with_cache(mocker, default_conf, time_machine) -> None:
     res = exchange.refresh_ohlcv_with_cache(pairs, start.timestamp())
     assert ohlcv_mock.call_count == 1
     assert len(ohlcv_mock.call_args_list[0][0][0]) == 1
+    assert len(res) == 5
 
     # Expire 5m and 1h cache
     time_machine.move_to(start + timedelta(hours=2), tick=False)
@@ -2829,6 +2831,7 @@ def test_refresh_ohlcv_with_cache(mocker, default_conf, time_machine) -> None:
     res = exchange.refresh_ohlcv_with_cache(pairs, start.timestamp())
     assert ohlcv_mock.call_count == 1
     assert len(ohlcv_mock.call_args_list[0][0][0]) == 2
+    assert len(res) == 5
 
     # Expire all caches
     time_machine.move_to(start + timedelta(days=1, hours=2), tick=False)
@@ -2838,6 +2841,7 @@ def test_refresh_ohlcv_with_cache(mocker, default_conf, time_machine) -> None:
     assert ohlcv_mock.call_count == 1
     assert len(ohlcv_mock.call_args_list[0][0][0]) == 5
     assert ohlcv_mock.call_args_list[0][0][0] == pairs
+    assert len(res) == 5
 
 
 def test_refresh_latest_ohlcv_funding_rate(mocker, default_conf_usdt, caplog) -> None: