fix: centralize tick price validation in calculate_spread_ratio and determine_order_limits (#52)

Replaces manual isinstance/<=0 checks in calculate_spread_ratio() and
determine_order_limits() with _valid_tick_price(), ensuring NaN, inf,
-inf, zero, negative, bool, and invalid-string tick values are
consistently rejected across all trading helpers.

Adds regression tests covering numeric-string acceptance and every
invalid-value category for both functions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mt5cli/trading.py

@@ -782,18 +782,15 @@ def calculate_spread_ratio(client: Mt5TradingClient, symbol: str) -> float:
     """Return ``(ask - bid) / ((ask + bid) / 2)`` for the latest tick.
 
     Raises:
-        Mt5TradingError: If bid or ask is unavailable or non-positive.
+        Mt5TradingError: If bid or ask is unavailable.
     """
     tick = get_tick_snapshot(client, symbol)
-    bid = tick.get("bid")
-    ask = tick.get("ask")
-    if not isinstance(bid, int | float) or not isinstance(ask, int | float):
+    bid = _valid_tick_price(tick, "bid")
+    ask = _valid_tick_price(tick, "ask")
+    if bid is None or ask is None:
         msg = f"Tick bid/ask is unavailable for {symbol!r}."
         raise Mt5TradingError(msg)
-    if bid <= 0 or ask <= 0:
-        msg = f"Tick bid/ask must be positive for {symbol!r}."
-        raise Mt5TradingError(msg)
-    return (float(ask) - float(bid)) / ((float(ask) + float(bid)) / 2.0)
+    return (ask - bid) / ((ask + bid) / 2.0)
 
 
 def calculate_new_position_margin_ratio(
@@ -1003,11 +1000,11 @@ def determine_order_limits(
     _require_protective_ratio(take_profit_ratio, "take_profit_limit_ratio")
     normalized_side = _position_side_from_order_side(side)
     tick = get_tick_snapshot(client, symbol)
-    entry_value = tick["ask"] if normalized_side == "long" else tick["bid"]
-    if not isinstance(entry_value, int | float):
+    entry_key = "ask" if normalized_side == "long" else "bid"
+    entry = _valid_tick_price(tick, entry_key)
+    if entry is None:
         msg = f"Tick price is unavailable for {symbol!r}."
         raise Mt5TradingError(msg)
-    entry = float(entry_value)
     try:
         symbol_info = get_symbol_snapshot(client, symbol)
     except (AttributeError, KeyError, TypeError, ValueError):

tests/test_trading.py

@@ -427,6 +427,55 @@ class TestDetermineOrderLimits:
         with pytest.raises(Mt5TradingError, match="Tick price is unavailable"):
             determine_order_limits(client, "EURUSD", "long")
 
+    def test_accepts_numeric_string_entry(self) -> None:
+        """Test numeric string ask/bid values are accepted as entry prices."""
+        client = MagicMock()
+        client.symbol_info_tick_as_dict.return_value = {
+            "ask": "1.1010",
+            "bid": "1.1000",
+        }
+        client.symbol_info_as_dict.return_value = {"digits": 4}
+
+        result = determine_order_limits(client, "EURUSD", "long")
+
+        _assert_close(result["entry"], 1.1010)
+
+    @pytest.mark.parametrize(
+        ("side", "field", "bad_value"),
+        [
+            ("long", "ask", float("nan")),
+            ("long", "ask", float("inf")),
+            ("long", "ask", float("-inf")),
+            ("long", "ask", 0.0),
+            ("long", "ask", -1.0),
+            ("long", "ask", True),
+            ("long", "ask", False),
+            ("long", "ask", "invalid"),
+            ("short", "bid", float("nan")),
+            ("short", "bid", float("inf")),
+            ("short", "bid", float("-inf")),
+            ("short", "bid", 0.0),
+            ("short", "bid", -1.0),
+            ("short", "bid", True),
+            ("short", "bid", False),
+            ("short", "bid", "invalid"),
+        ],
+    )
+    def test_rejects_invalid_entry_tick_values(
+        self,
+        side: str,
+        field: str,
+        bad_value: object,
+    ) -> None:
+        """Test invalid entry tick values raise Mt5TradingError."""
+        tick: dict[str, object] = {"ask": 1.1, "bid": 1.0}
+        tick[field] = bad_value
+        client = MagicMock()
+        client.symbol_info_tick_as_dict.return_value = tick
+
+        with pytest.raises(Mt5TradingError, match="Tick price is unavailable"):
+            determine_order_limits(client, "EURUSD", side)
+
     def test_rejects_stop_loss_inside_broker_stop_level(self) -> None:
         """Test stop-loss prices closer than trade_stops_level raise Mt5TradingError."""
         client = MagicMock()
@@ -793,6 +842,50 @@ class TestSnapshotsAndState:
         with pytest.raises(Mt5TradingError):
             calculate_spread_ratio(client, "EURUSD")
 
+    def test_calculate_spread_ratio_accepts_numeric_string_tick(self) -> None:
+        """Test numeric string bid/ask values are accepted."""
+        client = MagicMock()
+        client.symbol_info_tick_as_dict.return_value = {"bid": "99.0", "ask": "101.0"}
+
+        _assert_close(calculate_spread_ratio(client, "EURUSD"), 0.02)
+
+    @pytest.mark.parametrize(
+        ("field", "bad_value"),
+        [
+            ("bid", None),
+            ("bid", float("nan")),
+            ("bid", float("inf")),
+            ("bid", float("-inf")),
+            ("bid", 0.0),
+            ("bid", -1.0),
+            ("bid", True),
+            ("bid", False),
+            ("bid", "invalid"),
+            ("ask", None),
+            ("ask", float("nan")),
+            ("ask", float("inf")),
+            ("ask", float("-inf")),
+            ("ask", 0.0),
+            ("ask", -1.0),
+            ("ask", True),
+            ("ask", False),
+            ("ask", "invalid"),
+        ],
+    )
+    def test_calculate_spread_ratio_rejects_invalid_tick_values(
+        self,
+        field: str,
+        bad_value: object,
+    ) -> None:
+        """Test invalid bid/ask values raise Mt5TradingError."""
+        tick: dict[str, object] = {"bid": 100.0, "ask": 100.0}
+        tick[field] = bad_value
+        client = MagicMock()
+        client.symbol_info_tick_as_dict.return_value = tick
+
+        with pytest.raises(Mt5TradingError, match="Tick bid/ask is unavailable"):
+            calculate_spread_ratio(client, "EURUSD")
+
 
 class TestNormalizeOrderVolume:
     """Tests for normalize_order_volume."""