Fix clippy::format-push-string

idna/tests/uts46.rs

@@ -8,6 +8,7 @@
 
 use crate::test::TestFn;
 use std::char;
+use std::fmt::Write;
 
 use idna::Errors;
 
@@ -160,8 +161,7 @@ fn unescape(input: &str) -> String {
                             match char::from_u32(((c1 * 16 + c2) * 16 + c3) * 16 + c4) {
                                 Some(c) => output.push(c),
                                 None => {
-                                    output
-                                        .push_str(&format!("\\u{:X}{:X}{:X}{:X}", c1, c2, c3, c4));
+                                    write!(&mut output,"\\u{:X}{:X}{:X}{:X}", c1, c2, c3, c4).expect("Could not write to output");
                                 }
                             };
                         }