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: tests.rs
    path of file: ./repos/ink/crates/env/src/engine/off_chain
    
    the code of the file until where you have to start completion: // Copyright (C) Parity Technologies
    
fn topics_builder() -> Result<()> {
    crate::test::run_test::<crate::DefaultEnvironment, _>(|_| {
        // given
        let mut builder = TopicsBuilder::default();

        // when
        TopicsBuilderBackend::<crate::DefaultEnvironment>::push_topic(&mut builder, &13);
        TopicsBuilderBackend::<crate::DefaultEnvironment>::push_topic(&mut builder, &17);

        // then
        assert_eq!(builder.topics.len(), 2);

        let topics_len_compact = &scale::Compact(2u32);
        let topics_len_encoded = scale::Encode::encode(&topics_len_compact);
        let output = TopicsBuilderBackend::<crate::DefaultEnvironment>::output(builder);
        #[rustfmt::skip]
        let expected = vec![topics_len_encoded[0], 13, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 17, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
        assert_eq!(output, expected);

        Ok(())
    })
}