You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: substitute_alternate_syntax.rs
    path of file: ./repos/oxc/crates/oxc_minifier/tests/closure
    
    the code of the file until where you have to start completion: //! <https://github.com/google/closure-compiler/blob/master/test/com/google/javascript/jscomp/PeepholeSubstituteAlternateSyntaxTest.java>

use crate::test;

#[test]
fn fold_return_result() {
    test("function f(){return !1;}", "function f(){return !1}");
    test("function f(){return null;}", "function f(){return null}");
    test
    
fn undefined() {
    test("var x = undefined", "var x;");
    test(
        "var undefined = 1;function f() {var undefined=2;var x;}",
        "var undefined=1;function f(){var undefined=2,x}",
    );
    test("function f(undefined) {}", "function f(undefined){}");
    test("try {} catch(undefined) {}", "try{}catch(undefined){}");
    test("for (undefined in {}) {}", "for(undefined in {}){}");
    test("undefined++", "undefined++;");
    test("undefined += undefined;", "(undefined+=void 0);");
}