Repository: tokio-rs/tokio
File: tokio/tests/fs_link.rs (Rust)

Code before:
    std::fs::File::create(&src)
        .unwrap()
        .write_all(b"new-data")
        .unwrap();

    let content = fs::read(&dst).await.unwrap();
    assert_eq!(content, b"new-data");

    let read = fs::read_link(dst.clone()).await.unwrap();
    assert!(read == src);

    let symlink_meta = fs::symlink_metadata(dst.clone()).await.unwrap();
    assert!(symlink_meta.file_type().is_symlink());
}

#[tokio::test]
#[cfg_attr(miri, ignore)] // No `linkat` in miri.
async fn test_hard_link_error_source_not_found() {
    let dir = tempdir().unwrap();
    let src = dir.path().join("nonexistent.txt");
    let dst = dir.path().join("dst.txt");

    let result = fs::hard_link(&src, &dst).await;

    assert!(result.is_err());
    let err = result.unwrap_err();
    assert_eq!(err.kind(), std::io::ErrorKind::NotFound);
}

#[tokio::test]
#[cfg_attr(miri, ignore)] // No `linkat` in miri.
async fn test_hard_link_error_destination_already_exists() {
    let dir = tempdir().unwrap();
    let src = dir.path().join("src.txt");
    let dst = dir.path().join("dst.txt");

    // Create source file
    std::fs::File::create(&src)
        .unwrap()
        .write_all(b"source content")
        .unwrap();

    // Create destination file
    std::fs::File::create(&dst)
        .unwrap()
        .write_all(b"destination content")
        .unwrap();

    // Attempt to create hard link when destination already exists
    let result = fs::hard_link(&src, &dst).await;


Review comment (suggestion):
I believe `unwrap_err()` will give a better error message than your assert if the `Result` is `Ok`.
```suggestion
    let err = result.unwrap_err();
```

Code after:
    std::fs::File::create(&src)
        .unwrap()
        .write_all(b"new-data")
        .unwrap();

    let content = fs::read(&dst).await.unwrap();
    assert_eq!(content, b"new-data");

    let read = fs::read_link(dst.clone()).await.unwrap();
    assert!(read == src);

    let symlink_meta = fs::symlink_metadata(dst.clone()).await.unwrap();
    assert!(symlink_meta.file_type().is_symlink());
}

#[tokio::test]
#[cfg_attr(miri, ignore)] // No `linkat` in miri.
async fn test_hard_link_error_source_not_found() {
    let dir = tempdir().unwrap();
    let src = dir.path().join("nonexistent.txt");
    let dst = dir.path().join("dst.txt");

    let err = fs::hard_link(&src, &dst).await.unwrap_err();
    assert_eq!(err.kind(), std::io::ErrorKind::NotFound);
}

#[tokio::test]
#[cfg_attr(miri, ignore)] // No `linkat` in miri.
async fn test_hard_link_error_destination_already_exists() {
    let dir = tempdir().unwrap();
    let src = dir.path().join("src.txt");
    let dst = dir.path().join("dst.txt");

    // Create source file
    std::fs::write(&src, b"source content").unwrap();

    // Create destination file
    std::fs::write(&dst, b"destination content").unwrap();

    // Attempt to create hard link when destination already exists
    let err = fs::hard_link(&src, &dst).await.unwrap_err();
    assert_eq!(err.kind(), std::io::ErrorKind::AlreadyExists);
}

#[tokio::test]
#[cfg_attr(miri, ignore)] // No `linkat` in miri.
async fn test_hard_link_error_source_is_directory() {
    let dir = tempdir().unwrap();
    let src_dir = dir.path().join("src_directory");
    let dst = dir.path().join("dst.txt");