Add a validation check to prevent positive quantity

Signed-off-by: camille-bouvy-frequenz <[email protected]>

Author: camille-bouvy-frequenz

src/frequenz/client/electricity_trading/_client.py

@@ -404,6 +404,8 @@ def validate_params(
             validate_decimal_places(price.amount, PRECISION_DECIMAL_PRICE, "price")
         if not isinstance(quantity, _Sentinel) and quantity is not None:
             validate_decimal_places(quantity.mw, PRECISION_DECIMAL_QUANTITY, "quantity")
+            if quantity.mw <= 0:
+                raise ValueError("Quantity must be positive")
         if not isinstance(stop_price, _Sentinel) and stop_price is not None:
             raise NotImplementedError(
                 "STOP_LIMIT orders are not supported yet, so stop_price cannot be set."