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: mod.rs
    path of file: ./repos/gotham/gotham/src/pipeline
    
    the code of the file until where you have to start completion: //! Defines types for a middleware pipeline

mod chain;
pub use chain::PipelineHandleChain;

mod set;
pub use set::{finalize_pipeline_set, new_pipeline_set, EditablePipelineSet, PipelineSet};

mod single;
pub use single::{single_pipeline, SinglePipelineChain, SinglePipelineHandle, SinglePipelineSet};

use log::trace;
use std::pin::Pin;

use crate::handler:
    
/// fn main() {
///     let (chain, pipelines) = single_pipeline(
///         new_pipeline()
///             .add(MiddlewareOne)
///             .add(MiddlewareTwo)
///             .add(MiddlewareThree)
///             .build(),
///     );
///
///     let router = build_router(chain, pipelines, |route| {
///         route.get("/").to(handler);
///     });
///
///     let test_server = TestServer::new(router).unwrap();
///     let response = test_server
///         .client()
///         .get("http://example.com/")
///         .perform()
///         .unwrap();
///     assert_eq!(response.status(), StatusCode::OK);
///     assert_eq!(response.read_utf8_body().unwrap(), "[1, 2, 3]");
/// }