Fix warning for test-only helper method

src/syntax.rs

@@ -246,10 +246,6 @@ impl<'a> Syntax<'a> {
         self.info().num_ancestors.get()
     }
 
-    pub fn change(&'a self) -> Option<ChangeKind<'a>> {
-        self.info().change.get()
-    }
-
     pub fn first_line(&self) -> Option<LineNumber> {
         let position = match self {
             List { open_position, .. } => open_position,
@@ -795,6 +791,12 @@ mod tests {
     use super::*;
     use pretty_assertions::assert_eq;
 
+    impl<'a> Syntax<'a> {
+        pub fn change(&'a self) -> Option<ChangeKind<'a>> {
+            self.info().change.get()
+        }
+    }
+
     #[test]
     fn test_comment_and_atom_differ() {
         let pos = vec![SingleLineSpan {