fix: Add test for StyleVariableHolder

src/formatter/model.rs

@@ -81,6 +81,10 @@ impl<'a> StyleVariableHolder<Cow<'a, str>> for Vec<FormatElement<'a>> {
                 acc.extend(textgroup.style.get_style_variables());
                 acc
             }
+            FormatElement::Positional(format) => {
+                acc.extend(format.get_style_variables());
+                acc
+            }
             _ => acc,
         })
     }

src/formatter/string_formatter.rs

@@ -408,6 +408,16 @@ mod tests {
         assert_eq!(variables, expected_variables);
     }
 
+    #[test]
+    fn test_style_variable_holder() {
+        const FORMAT_STR: &str = "($a [($b) $c](none $s)) $d [t]($t)";
+        let expected_variables = BTreeSet::from_iter(vec!["s", "t"].into_iter().map(String::from));
+
+        let formatter = StringFormatter::new(FORMAT_STR).unwrap().map(empty_mapper);
+        let variables = formatter.get_style_variables();
+        assert_eq!(variables, expected_variables);
+    }
+
     #[test]
     fn test_parse_error() {
         // brackets without escape