Fixed FormattingRules not being applied

tests/core/formatting/test_engine.py

@@ -350,3 +350,32 @@ class TestPresets:
 
         assert "background-color: purple" in css.css
         assert "color: yellow" in css.css
+
+    def test_i_can_expand_rule_preset_via_style(self):
+        """A rule preset referenced via style() must be expanded like via format().
+
+        Why: style("traffic_light") should expand the traffic_light rule preset
+        (which has conditional style rules) instead of looking up "traffic_light"
+        as a style preset name (where it doesn't exist).
+        """
+        engine = FormattingEngine()
+        rules = [FormatRule(style=Style(preset="traffic_light"))]
+
+        css, _ = engine.apply_format(rules, cell_value=-5)
+
+        assert css is not None
+        assert css.cls == "mf-formatting-error"
+
+    def test_i_can_expand_rule_preset_via_style_with_no_match(self):
+        """A rule preset via style() with a non-matching condition returns no style.
+
+        Why: traffic_light has style("error") only if value < 0.
+        A positive value should produce no style output.
+        """
+        engine = FormattingEngine()
+        rules = [FormatRule(style=Style(preset="traffic_light"))]
+
+        css, _ = engine.apply_format(rules, cell_value=10)
+
+        assert css is not None
+        assert css.cls == "mf-formatting-success"