Add NoDbContext context manager

tests/persistence/test_db_context.py

@@ -0,0 +1,24 @@
+import pytest
+
+from freqtrade.persistence import FtNoDBContext, PairLocks, Trade
+
+
+@pytest.mark.parametrize('timeframe', ['', '5m', '1d'])
+def test_FtNoDBContext(timeframe):
+    assert Trade.use_db is True
+    assert PairLocks.use_db is True
+    assert PairLocks.timeframe == ''
+
+    with FtNoDBContext(timeframe):
+        assert Trade.use_db is False
+        assert PairLocks.use_db is False
+        assert PairLocks.timeframe == timeframe
+
+    with FtNoDBContext():
+        assert Trade.use_db is False
+        assert PairLocks.use_db is False
+        assert PairLocks.timeframe == ''
+
+    assert Trade.use_db is True
+    assert PairLocks.use_db is True
+