divbuf 0.4.1

// vim: tw=80

use std::{
    borrow::{Borrow, BorrowMut},
    cmp::Ordering,
    collections::hash_map::DefaultHasher,
    convert::TryInto,
    hash::{Hash, Hasher},
    io::Write,
    thread,
};

use divbuf::*;
use lazy_static::lazy_static;

fn simple_hash<T: Hash>(t: &T) -> u64 {
    let mut s = DefaultHasher::new();
    t.hash(&mut s);
    s.finish()
}

//
// Chunks methods
//
mod chunks {
    use super::*;

    #[test]
    pub fn iter() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let db = dbs.try_const().unwrap();
        let mut chunks = db.into_chunks(3);
        assert_eq!(&chunks.next().unwrap()[..], &[1, 2, 3][..]);
        assert_eq!(&chunks.next().unwrap()[..], &[4, 5, 6][..]);
        assert!(chunks.next().is_none());
    }

    #[test]
    #[should_panic]
    pub fn zero() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let db = dbs.try_const().unwrap();
        db.into_chunks(0);
    }

    #[test]
    pub fn size_hint() {
        let dbs =
            DivBufShared::from(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(1).size_hint(),
            (12, Some(12))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(2).size_hint(),
            (6, Some(6))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(3).size_hint(),
            (4, Some(4))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(4).size_hint(),
            (3, Some(3))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(5).size_hint(),
            (3, Some(3))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(6).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(7).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(8).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(9).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(10).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(11).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_const().unwrap().into_chunks(12).size_hint(),
            (1, Some(1))
        );
    }
}

//
// ChunksMut methods
//
mod chunks_mut {
    use super::*;

    #[test]
    pub fn iter() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let dbm = dbs.try_mut().unwrap();
        let mut chunks = dbm.into_chunks(3);
        assert_eq!(&chunks.next().unwrap()[..], &[1, 2, 3][..]);
        assert_eq!(&chunks.next().unwrap()[..], &[4, 5, 6][..]);
        assert!(chunks.next().is_none());
    }

    #[test]
    #[should_panic]
    pub fn zero() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let dbm = dbs.try_mut().unwrap();
        dbm.into_chunks(0);
    }

    #[test]
    pub fn size_hint() {
        let dbs =
            DivBufShared::from(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(1).size_hint(),
            (12, Some(12))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(2).size_hint(),
            (6, Some(6))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(3).size_hint(),
            (4, Some(4))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(4).size_hint(),
            (3, Some(3))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(5).size_hint(),
            (3, Some(3))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(6).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(7).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(8).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(9).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(10).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(11).size_hint(),
            (2, Some(2))
        );
        assert_eq!(
            dbs.try_mut().unwrap().into_chunks(12).size_hint(),
            (1, Some(1))
        );
    }
}

//
// DivBufShared methods
//
mod divbufshared {
    use super::*;

    #[test]
    pub fn cap_and_len() {
        let mut v = Vec::<u8>::with_capacity(64);
        v.push(0);
        let dbs = DivBufShared::from(v);
        assert_eq!(dbs.capacity(), 64);
        assert_eq!(dbs.len(), 1);
    }

    #[test]
    pub fn fmt() {
        let v = Vec::<u8>::with_capacity(64);
        let dbs = DivBufShared::from(v);
        let output = format!("{:?}", &dbs);
        let expected = "DivBufShared { inner: Inner { vec: [], accessors: 0, \
                        sharers: 1 } }";
        assert_eq!(output, expected);
    }

    #[test]
    pub fn from_slice() {
        let s = b"abcdefg";
        let dbs = DivBufShared::from(&s[..]);
        let mut dbm = dbs.try_mut().unwrap();
        assert_eq!(dbm, s[..]);
        // dbs should've been copy constructed, so we can mutate it without changing
        // the original slice
        dbm[0] = b'A';
        assert_ne!(dbm, s[..]);
    }

    #[test]
    pub fn is_empty() {
        assert!(DivBufShared::with_capacity(4096).is_empty());
        assert!(!DivBufShared::from(vec![1, 2, 3]).is_empty());
    }

    #[test]
    pub fn send() {
        let dbs = DivBufShared::with_capacity(4096);
        thread::spawn(move || {
            let _ = dbs;
        })
        .join()
        .unwrap();
    }

    #[test]
    pub fn sync() {
        lazy_static! {
            pub static ref DBS: DivBufShared =
                DivBufShared::from(vec![0; 4096]);
        }
        let r = &DBS;
        thread::spawn(move || {
            let _ = r;
        })
        .join()
        .unwrap();
    }

    #[test]
    pub fn try_const() {
        let dbs = DivBufShared::with_capacity(4096);
        // Create an initial DivBuf
        let _db0 = dbs.try_const().unwrap();
        // Creating a second is allowed, too
        let _db1 = dbs.try_const().unwrap();
    }

    #[test]
    pub fn try_const_after_try_mut() {
        let dbs = DivBufShared::with_capacity(4096);
        // Create an initial DivBufMut
        let _dbm = dbs.try_mut().unwrap();
        // Creating a DivBuf should fail, because there are writers
        assert!(dbs.try_const().is_err());
    }

    #[test]
    pub fn try_mut() {
        let dbs = DivBufShared::with_capacity(4096);
        // Create an initial DivBufMut
        let _dbm0 = dbs.try_mut().unwrap();
        // Creating a second is not allowed
        assert!(dbs.try_mut().is_err());
    }

    #[test]
    pub fn try_mut_after_try_const() {
        let dbs = DivBufShared::with_capacity(4096);
        // Create an initial DivBuf
        let _db0 = dbs.try_const().unwrap();
        // Now creating a mutable buffer is not allowed
        assert!(dbs.try_mut().is_err());
    }

    #[cfg(feature = "experimental")]
    #[test]
    pub fn uninitialized() {
        let cap = 4096;
        let dbs = DivBufShared::uninitialized(cap);
        assert_eq!(dbs.capacity(), cap);
        assert_eq!(dbs.len(), cap);
    }

    #[test]
    pub fn to_vec() {
        let v = vec![1, 2, 3, 4];
        let dbs = DivBufShared::from(v);

        {
            let mut dbm = dbs.try_mut().unwrap();
            assert_eq!(dbm, [1, 2, 3, 4][..]);
            dbm[0] = 5;
            assert_eq!(dbm, [5, 2, 3, 4][..]);
        }

        let v2: Vec<u8> = dbs.try_into().unwrap();
        assert_eq!(v2, vec![5, 2, 3, 4]);
    }

    #[test]
    pub fn to_vec_after_try_mut() {
        let v = vec![1, 2, 3, 4];
        let dbs = DivBufShared::from(v);

        let _dbm = dbs.try_mut().unwrap();
        let maybe_v: Result<Vec<u8>, _> = dbs.try_into();
        assert!(maybe_v.is_err());
    }

    #[test]
    pub fn to_vec_after_try_const() {
        let v = vec![1, 2, 3, 4];
        let dbs = DivBufShared::from(v);

        let _db = dbs.try_const().unwrap();
        let maybe_v: Result<Vec<u8>, _> = dbs.try_into();
        assert!(maybe_v.is_err());
    }

    #[test]
    pub fn to_vec_after_clone_inaccessible() {
        let v = vec![1, 2, 3, 4];
        let dbs = DivBufShared::from(v);

        let dbm = dbs.try_mut().unwrap();
        let _dbi = dbm.clone_inaccessible();
        drop(dbm);

        let maybe_v: Result<Vec<u8>, _> = dbs.try_into();
        assert!(maybe_v.is_err());
    }
}

//
// DivBuf methods
//
mod divbuf_ {
    use super::*;

    #[test]
    pub fn as_ref() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let db0 = dbs.try_const().unwrap();
        let s: &[u8] = db0.as_ref();
        assert_eq!(s, &[1, 2, 3]);
    }

    #[test]
    pub fn as_ref_empty() {
        let dbs = DivBufShared::from(vec![]);
        let db0 = dbs.try_const().unwrap();
        let s: &[u8] = db0.as_ref();
        assert_eq!(s, &[]);
    }

    #[test]
    pub fn borrow() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let db0 = dbs.try_const().unwrap();
        let s: &[u8] = db0.borrow();
        assert_eq!(s, &[1, 2, 3]);
    }

    #[test]
    pub fn clone() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let db0 = dbs.try_const().unwrap();
        let mut db1 = db0.clone();
        assert_eq!(db0, db1);
        // We should be able to modify one DivBuf without affecting the other
        db1.split_off(1);
        assert_ne!(db0, db1);
    }

    #[test]
    pub fn clone_inaccessible() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let dbm = dbs.try_mut().unwrap();
        let _dbi: DivBufInaccessible = dbm.clone_inaccessible();
    }

    #[test]
    pub fn deref() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let db = dbs.try_const().unwrap();
        let slice: &[u8] = &db;
        assert_eq!(slice, &[1, 2, 3]);
    }

    #[test]
    pub fn deref_empty() {
        let dbs = DivBufShared::from(vec![]);
        let db = dbs.try_const().unwrap();
        let slice: &[u8] = &db;
        assert_eq!(slice, &[]);
    }

    // A DivBuf should be able to own its storage, and will free it on last drop
    #[test]
    pub fn drop_last() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let _db0 = dbs0.try_const().unwrap();
        drop(dbs0);
    }

    #[test]
    pub fn eq() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let dbs1 = DivBufShared::from(vec![1, 2, 3]);
        let dbs2 = DivBufShared::from(vec![1, 2]);
        let db0 = dbs0.try_const().unwrap();
        let db1 = dbs1.try_const().unwrap();
        let db2 = dbs2.try_const().unwrap();
        assert_eq!(db0, db1);
        assert_ne!(db0, db2);
    }

    #[test]
    pub fn from_divbufmut() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let dbm = dbs.try_mut().unwrap();
        let _db = DivBuf::from(dbm);
    }

    #[test]
    pub fn is_empty() {
        let dbs0 = DivBufShared::with_capacity(64);
        let db0 = dbs0.try_const().unwrap();
        assert!(db0.is_empty());

        let dbs1 = DivBufShared::from(vec![1]);
        let db1 = dbs1.try_const().unwrap();
        assert!(!db1.is_empty());
    }

    #[test]
    pub fn hash() {
        let v = vec![1, 2, 3, 4, 5, 6];
        let expected = simple_hash(&v);
        let dbs = DivBufShared::from(v);
        let db0 = dbs.try_const().unwrap();
        assert_eq!(simple_hash(&db0), expected);
    }

    #[test]
    pub fn ord() {
        let dbs = DivBufShared::from(vec![0, 1, 0, 2]);
        let db0 = dbs.try_const().unwrap().slice_to(2);
        let db1 = dbs.try_const().unwrap().slice_from(2);
        assert_eq!(db0.cmp(&db1), Ordering::Less);
    }

    #[test]
    pub fn partial_ord() {
        let dbs = DivBufShared::from(vec![0, 1, 0, 2]);
        let db0 = dbs.try_const().unwrap().slice_to(2);
        let db1 = dbs.try_const().unwrap().slice_from(2);
        assert!(db0 < db1);
    }

    #[test]
    pub fn send() {
        let dbs = DivBufShared::with_capacity(4096);
        let db = dbs.try_const().unwrap();
        thread::spawn(move || {
            let _ = db;
        })
        .join()
        .unwrap();
    }

    #[test]
    pub fn sync() {
        lazy_static! {
            pub static ref DBS: DivBufShared =
                DivBufShared::from(vec![0; 4096]);
            pub static ref DB: DivBuf = DBS.try_const().unwrap();
        }
        let r = &DB;
        thread::spawn(move || {
            let _ = r;
        })
        .join()
        .unwrap();
    }

    #[test]
    pub fn slice() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let db0 = dbs.try_const().unwrap();
        assert_eq!(db0.slice(0, 0), [][..]);
        assert_eq!(db0.slice(1, 5), [2, 3, 4, 5][..]);
        assert_eq!(db0.slice(1, 1), [][..]);
        assert_eq!(db0.slice(0, 6), db0);
        assert_eq!(db0, [1, 2, 3, 4, 5, 6][..]);
    }

    #[test]
    #[should_panic(expected = "begin <= end")]
    pub fn slice_backwards() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let db0 = dbs.try_const().unwrap();
        db0.slice(1, 0);
    }

    #[test]
    #[should_panic(expected = "end <= self.len")]
    pub fn slice_after_end() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let db0 = dbs.try_const().unwrap();
        db0.slice(3, 7);
    }

    #[test]
    pub fn slice_from() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let db0 = dbs.try_const().unwrap();
        assert_eq!(db0.slice_from(0), db0);
        assert_eq!(db0.slice_from(3), [4, 5, 6][..]);
    }

    #[test]
    pub fn slice_to() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let db0 = dbs.try_const().unwrap();
        assert_eq!(db0.slice_to(6), db0);
        assert_eq!(db0.slice_to(3), [1, 2, 3][..]);
    }

    #[test]
    pub fn split_off() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut db0 = dbs.try_const().unwrap();
        // split in the middle
        let db_mid = db0.split_off(4);
        assert_eq!(db0, [1, 2, 3, 4][..]);
        assert_eq!(db0.len(), 4);
        assert_eq!(db_mid, [5, 6][..]);
        assert_eq!(db_mid.len(), 2);
        // split at the beginning
        let mut db_begin = db0.split_off(0);
        assert_eq!(db0, [][..]);
        assert_eq!(db_begin, [1, 2, 3, 4][..]);
        // split at the end
        let db_end = db_begin.split_off(4);
        assert_eq!(db_begin, [1, 2, 3, 4][..]);
        assert_eq!(db_end, [][..]);
    }

    #[test]
    #[should_panic(expected = "Can't split past the end")]
    pub fn split_off_past_the_end() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut db0 = dbs.try_const().unwrap();
        db0.split_off(7);
    }

    #[test]
    pub fn split_to() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut db0 = dbs.try_const().unwrap();
        // split in the middle
        let mut db_left = db0.split_to(4);
        assert_eq!(db_left, [1, 2, 3, 4][..]);
        assert_eq!(db_left.len(), 4);
        assert_eq!(db0, [5, 6][..]);
        assert_eq!(db0.len(), 2);
        // split at the beginning
        let db_begin = db_left.split_to(0);
        assert_eq!(db_begin, [][..]);
        assert_eq!(db_left, [1, 2, 3, 4][..]);
        // split at the end
        let db_mid = db_left.split_to(4);
        assert_eq!(db_mid, [1, 2, 3, 4][..]);
        assert_eq!(db_left, [][..]);
    }

    #[test]
    #[should_panic(expected = "Can't split past the end")]
    pub fn split_to_past_the_end() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut db0 = dbs.try_const().unwrap();
        db0.split_to(7);
    }

    #[test]
    pub fn try_mut() {
        let dbs = DivBufShared::with_capacity(64);
        let mut db0 = dbs.try_const().unwrap();
        db0 = {
            let db1 = dbs.try_const().unwrap();
            // When multiple DivBufs are active, none can be upgraded
            let db2 = db0.try_mut();
            assert!(db2.is_err());
            let db3 = db1.try_mut();
            assert!(db3.is_err());
            db2.unwrap_err()
        };
        // A single DivBuf alone can be upgraded
        assert!(db0.try_mut().is_ok());
    }

    #[test]
    pub fn unsplit() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut db0 = dbs0.try_const().unwrap();
        {
            // split in the middle
            let db_mid = db0.split_off(4);
            // put it back together
            assert!(db0.unsplit(db_mid).is_ok());
            assert_eq!(db0, [1, 2, 3, 4, 5, 6][..]);
        }

        {
            // unsplit should fail for noncontiguous DivBufs
            let mut db_begin = db0.slice_to(2);
            let db_end = db0.slice_from(4);
            assert!(db_begin.unsplit(db_end).is_err());
        }

        {
            // unsplit should fail for overlapping DivBufs
            let mut db_begin = db0.slice_to(4);
            let db_end = db0.slice_from(2);
            assert!(db_begin.unsplit(db_end).is_err());
        }

        {
            // unsplit should fail for unrelated DivBufs
            let dbs1 = DivBufShared::from(vec![7, 8, 9]);
            let mut db_end = db0.slice_from(4);
            let db_unrelated = dbs1.try_const().unwrap();
            assert!(db_end.unsplit(db_unrelated).is_err());
        }
    }
}

mod divbuf_inaccessible {
    use super::*;

    /// DivBufInaccessible's superpower is clone.
    #[test]
    #[allow(clippy::redundant_clone)]
    pub fn clone() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let db0 = dbs0.try_const().unwrap();
        let dbi0 = db0.clone_inaccessible();
        let _dbi1 = dbi0.clone();
    }

    // A DivBufInaccessible should be able to own its storage, and will free it
    // on last drop.
    #[test]
    pub fn drop_last() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let db0 = dbs0.try_const().unwrap();
        let _dbi = db0.clone_inaccessible();
        drop(db0);
        drop(dbs0);
    }

    #[test]
    pub fn send() {
        let dbs = DivBufShared::with_capacity(4096);
        let db = dbs.try_const().unwrap();
        let dbi = db.clone_inaccessible();
        thread::spawn(move || {
            let _ = dbi;
        })
        .join()
        .unwrap();
    }

    #[test]
    pub fn sync() {
        lazy_static! {
            pub static ref DBS: DivBufShared =
                DivBufShared::from(vec![0; 4096]);
            pub static ref DB: DivBuf = DBS.try_const().unwrap();
            pub static ref DBI: DivBufInaccessible = DB.clone_inaccessible();
        }
        let r = &DBI;
        thread::spawn(move || {
            let _ = r;
        })
        .join()
        .unwrap();
    }

    #[test]
    pub fn try_const_failure() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let dbm = dbs0.try_mut().unwrap();
        let dbi = dbm.clone_inaccessible();
        dbi.try_const().unwrap_err();
    }

    #[test]
    pub fn try_const_success() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let db0 = dbs0.try_const().unwrap();
        let dbi = db0.clone_inaccessible();
        dbi.try_const().unwrap();
    }

    #[test]
    pub fn try_mut_failure() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let db = dbs0.try_const().unwrap();
        let dbi = db.clone_inaccessible();
        dbi.try_mut().unwrap_err();
    }

    #[test]
    pub fn try_mut_success() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let db0 = dbs0.try_const().unwrap();
        let dbi = db0.clone_inaccessible();
        drop(db0);
        dbi.try_mut().unwrap();
    }
}

//
// DivBufMut methods
//
mod divbuf_mut {
    use super::*;

    #[test]
    pub fn as_ref() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let dbm0 = dbs.try_mut().unwrap();
        let s: &[u8] = dbm0.as_ref();
        assert_eq!(s, &[1, 2, 3]);
    }

    #[test]
    pub fn as_ref_empty() {
        let dbs = DivBufShared::from(vec![]);
        let dbm0 = dbs.try_mut().unwrap();
        let s: &[u8] = dbm0.as_ref();
        assert_eq!(s, &[]);
    }

    #[test]
    pub fn borrow() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let dbm0 = dbs.try_mut().unwrap();
        let s: &[u8] = dbm0.borrow();
        assert_eq!(s, &[1, 2, 3]);
    }

    #[test]
    pub fn borrowmut() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        {
            let mut dbm0 = dbs.try_mut().unwrap();
            let s: &mut [u8] = dbm0.borrow_mut();
            s[0] = 9;
        }
        let db0 = dbs.try_const().unwrap();
        let slice: &[u8] = &db0;
        assert_eq!(slice, &[9, 2, 3]);
    }

    #[test]
    pub fn clone_inaccessible() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let db = dbs.try_const().unwrap();
        let _dbi: DivBufInaccessible = db.clone_inaccessible();
    }

    #[test]
    pub fn deref() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let dbm = dbs.try_mut().unwrap();
        let slice: &[u8] = &dbm;
        assert_eq!(slice, &[1, 2, 3]);
    }

    #[test]
    pub fn deref_empty() {
        let dbs = DivBufShared::from(vec![]);
        let dbm = dbs.try_mut().unwrap();
        let slice: &[u8] = &dbm;
        assert_eq!(slice, &[]);
    }

    #[test]
    pub fn derefmut() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        let mut dbm = dbs.try_mut().unwrap();
        // Unlike DivBuf, we _can_ update DivBufMuts randomly
        dbm[0] = 9;
        let slice: &mut [u8] = &mut dbm;
        assert_eq!(slice, &[9, 2, 3]);
    }

    #[test]
    pub fn derefmut_empty() {
        let dbs = DivBufShared::from(vec![]);
        let mut dbm = dbs.try_mut().unwrap();
        let slice: &mut [u8] = &mut dbm;
        assert_eq!(slice, &[]);
    }

    // A DivBufMut should be able to own its storage, and will free it on last drop
    #[test]
    pub fn drop_last() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let _dbm0 = dbs0.try_mut().unwrap();
        drop(dbs0);
    }

    #[test]
    pub fn eq() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3]);
        let dbs1 = DivBufShared::from(vec![1, 2, 3]);
        let dbs2 = DivBufShared::from(vec![1, 2]);
        let dbm0 = dbs0.try_mut().unwrap();
        let dbm1 = dbs1.try_mut().unwrap();
        let dbm2 = dbs2.try_mut().unwrap();
        assert_eq!(dbm0, dbm1);
        assert_ne!(dbm0, dbm2);
    }

    #[test]
    pub fn extend() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        {
            let mut dbm = dbs.try_mut().unwrap();
            dbm.extend([4, 5, 6].iter());
        }
        // verify that dbs.inner.vec was extended
        let db = dbs.try_const().unwrap();
        let slice: &[u8] = &db;
        assert_eq!(slice, &[1, 2, 3, 4, 5, 6]);
    }

    #[test]
    #[should_panic(expected = "extend into the middle of a buffer")]
    pub fn extend_from_the_middle() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut dbm = dbs.try_mut().unwrap();
        let mut dbm_begin = dbm.split_to(3);
        dbm_begin.extend([7, 8, 9].iter());
    }

    #[test]
    pub fn freeze() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6, 7, 8]);
        {
            // Simplest case: freeze the entire buffer
            let dbm = dbs.try_mut().unwrap();
            let _: DivBuf = dbm.freeze();
        }
        {
            // Freeze a buffer in the presence of other readers && writers
            let mut dbm = dbs.try_mut().unwrap();
            let right_half = dbm.split_off(4);
            let _db_right_half = right_half.freeze();
            let left_quarter = dbm.split_to(2);
            let _db_left_quarter = left_quarter.freeze();
            // We should still be able to mutate from the remaining DivBufMut
            dbm[0] = 33;
        }
    }

    #[test]
    pub fn hash() {
        let v = vec![1, 2, 3, 4, 5, 6];
        let expected = simple_hash(&v);
        let dbs = DivBufShared::from(v);
        let dbm0 = dbs.try_mut().unwrap();
        assert_eq!(simple_hash(&dbm0), expected);
    }

    #[test]
    pub fn is_empty() {
        let dbs0 = DivBufShared::with_capacity(64);
        let mut dbm0 = dbs0.try_mut().unwrap();
        assert!(dbm0.is_empty());

        dbm0.extend([4, 5, 6].iter());
        assert!(!dbm0.is_empty());
    }

    #[test]
    pub fn ord() {
        let dbs = DivBufShared::from(vec![0, 1, 0, 2]);
        let mut dbm0 = dbs.try_mut().unwrap();
        let dbm1 = dbm0.split_off(2);
        assert_eq!(dbm0.cmp(&dbm1), Ordering::Less);
    }

    #[test]
    pub fn partial_ord() {
        let dbs = DivBufShared::from(vec![0, 1, 0, 2]);
        let mut dbm0 = dbs.try_mut().unwrap();
        let dbm1 = dbm0.split_off(2);
        assert!(dbm0 < dbm1);
    }

    #[test]
    pub fn reserve() {
        let v = Vec::<u8>::with_capacity(64);
        let dbs = DivBufShared::from(v);
        let mut dbm = dbs.try_mut().unwrap();
        dbm.reserve(128);
        assert_eq!(dbs.capacity(), 128);
    }

    #[test]
    #[should_panic(expected = "reserve from the middle of a buffer")]
    pub fn reserve_from_the_middle() {
        let v = vec![1, 2, 3, 4, 5, 6];
        let dbs = DivBufShared::from(v);
        let mut dbm = dbs.try_mut().unwrap();
        let mut left_half = dbm.split_to(3);
        left_half.reserve(128);
    }

    #[test]
    pub fn send() {
        let dbs = DivBufShared::with_capacity(4096);
        let dbm = dbs.try_mut().unwrap();
        thread::spawn(move || {
            let _ = dbm;
        })
        .join()
        .unwrap();
    }

    #[test]
    pub fn sync() {
        lazy_static! {
            pub static ref DBS: DivBufShared =
                DivBufShared::from(vec![0; 4096]);
            pub static ref DBM: DivBufMut = DBS.try_mut().unwrap();
        }
        let r = &DBM;
        thread::spawn(move || {
            let _ = r;
        })
        .join()
        .unwrap();
    }

    #[test]
    pub fn split_off() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut dbm0 = dbs.try_mut().unwrap();
        // split in the middle
        let dbm_mid = dbm0.split_off(4);
        assert_eq!(dbm0, [1, 2, 3, 4][..]);
        assert_eq!(dbm0.len(), 4);
        assert_eq!(dbm_mid, [5, 6][..]);
        assert_eq!(dbm_mid.len(), 2);
        // split at the beginning
        let mut dbm_begin = dbm0.split_off(0);
        assert_eq!(dbm0, [][..]);
        assert_eq!(dbm_begin, [1, 2, 3, 4][..]);
        // split at the end
        let dbm_end = dbm_begin.split_off(4);
        assert_eq!(dbm_begin, [1, 2, 3, 4][..]);
        assert_eq!(dbm_end, [][..]);
    }

    #[test]
    #[should_panic(expected = "Can't split past the end")]
    pub fn split_off_past_the_end() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut dbm0 = dbs.try_mut().unwrap();
        dbm0.split_off(7);
    }

    #[test]
    pub fn split_to() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut dbm0 = dbs.try_mut().unwrap();
        // split in the middle
        let mut dbm_left = dbm0.split_to(4);
        assert_eq!(dbm_left, [1, 2, 3, 4][..]);
        assert_eq!(dbm_left.len(), 4);
        assert_eq!(dbm0, [5, 6][..]);
        assert_eq!(dbm0.len(), 2);
        // split at the beginning
        let dbm_begin = dbm_left.split_to(0);
        assert_eq!(dbm_begin, [][..]);
        assert_eq!(dbm_left, [1, 2, 3, 4][..]);
        // split at the end
        let dbm_mid = dbm_left.split_to(4);
        assert_eq!(dbm_mid, [1, 2, 3, 4][..]);
        assert_eq!(dbm_left, [][..]);
    }

    #[test]
    #[should_panic(expected = "Can't split past the end")]
    pub fn split_to_past_the_end() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        let mut dbm0 = dbs.try_mut().unwrap();
        dbm0.split_to(7);
    }

    #[test]
    pub fn try_extend() {
        let dbs = DivBufShared::from(vec![1, 2, 3]);
        {
            let mut dbm0 = dbs.try_mut().unwrap();
            assert!(dbm0.try_extend([4, 5, 6].iter()).is_ok());

            // Extending from the middle of the vec should fail
            let mut dbm1 = dbm0.split_to(2);
            assert!(dbm1.try_extend([7, 8, 9].iter()).is_err());
        }

        // verify that dbs.inner.vec was extended the first time, but not the
        // second.
        let db = dbs.try_const().unwrap();
        assert_eq!(db, [1, 2, 3, 4, 5, 6][..]);
    }

    #[test]
    pub fn try_resize() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        {
            let mut dbm0 = dbs.try_mut().unwrap();
            // First, resize past the end of the vector
            assert!(dbm0.try_resize(7, 42).is_ok());
            assert_eq!(dbm0.len(), 7);
            assert_eq!(&dbm0[..], &[1, 2, 3, 4, 5, 6, 42][..]);
            // Then, do a truncation
            assert!(dbm0.try_resize(4, 42).is_ok());
            assert_eq!(dbm0, [1, 2, 3, 4][..]);
            // Check that the shared vector was truncated, too
            assert_eq!(dbs.len(), 4);
            // A resize of a non-terminal DivBufMut should fail
            let mut dbm1 = dbm0.split_to(2);
            assert!(dbm1.try_resize(3, 42).is_err());
            assert!(dbm1.try_resize(10, 42).is_err());
            assert_eq!(dbs.len(), 4);
            // Resizing a terminal DivBufMut should work, even if it doesn't start
            // at the vector's beginning
            assert!(dbm0.try_resize(5, 0).is_ok());
            assert_eq!(&dbm0[..], &[3, 4, 0, 0, 0][..]);
        }
    }

    #[test]
    pub fn try_truncate() {
        let dbs = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        {
            let mut dbm0 = dbs.try_mut().unwrap();
            // First, truncate past the end of the vector
            assert!(dbm0.try_truncate(7).is_ok());
            assert_eq!(dbm0.len(), 6);
            // Then, do a normal truncation
            assert!(dbm0.try_truncate(4).is_ok());
            assert_eq!(dbm0, [1, 2, 3, 4][..]);
            // Check that the shared vector was truncated, too
            assert_eq!(dbs.len(), 4);
            // A truncation of a non-terminal DivBufMut should fail
            let mut dbm1 = dbm0.split_to(2);
            assert!(dbm1.try_truncate(3).is_err());
            assert_eq!(dbs.len(), 4);
            // Truncating a terminal DivBufMut should work, even if it doesn't start
            // at the vector's beginning
            assert!(dbm0.try_truncate(1).is_ok());
            assert_eq!(dbs.len(), 3);
        }
    }

    #[test]
    pub fn unsplit() {
        let dbs0 = DivBufShared::from(vec![1, 2, 3, 4, 5, 6]);
        {
            let mut dbm0 = dbs0.try_mut().unwrap();
            // split in the middle
            let dbm_mid = dbm0.split_off(4);
            // put it back together
            assert!(dbm0.unsplit(dbm_mid).is_ok());
            assert_eq!(dbm0, [1, 2, 3, 4, 5, 6][..]);
        }

        {
            // unsplit should fail for noncontiguous DivBufMuts
            let mut dbm0 = dbs0.try_mut().unwrap();
            let mut dbm_begin = dbm0.split_to(2);
            let dbm_end = dbm0.split_off(2);
            assert!(dbm_begin.unsplit(dbm_end).is_err());
        }

        {
            // unsplit should fail for unrelated DivBufMuts
            let mut dbm0 = dbs0.try_mut().unwrap();
            let dbs1 = DivBufShared::from(vec![7, 8, 9]);
            let mut dbm_end = dbm0.split_off(4);
            let dbm_unrelated = dbs1.try_mut().unwrap();
            assert!(dbm_end.unsplit(dbm_unrelated).is_err());
        }
    }

    #[test]
    pub fn write() {
        const MSG: &[u8] = b"ABCD";
        let dbs0 = DivBufShared::with_capacity(0);
        let mut dbm0 = dbs0.try_mut().unwrap();
        assert_eq!(MSG.len(), dbm0.write(MSG).unwrap());
        assert_eq!(&dbm0[..], &[65u8, 66u8, 67u8, 68u8][..])
    }

    #[test]
    pub fn write_nonterminal() {
        let dbs0 = DivBufShared::from(vec![0, 1, 2, 3]);
        let mut dbm0 = dbs0.try_mut().unwrap();
        let _ = dbm0.split_off(2);
        assert!(dbm0.write("ABCD".as_bytes()).is_err());
    }

    #[test]
    pub fn write_all() {
        let dbs0 = DivBufShared::with_capacity(0);
        let mut dbm0 = dbs0.try_mut().unwrap();
        dbm0.write_all("ABCD".as_bytes()).unwrap();
        assert_eq!(&dbm0[..], &[65u8, 66u8, 67u8, 68u8][..])
    }

    #[test]
    pub fn write_all_nonterminal() {
        let dbs0 = DivBufShared::from(vec![0, 1, 2, 3]);
        let mut dbm0 = dbs0.try_mut().unwrap();
        let _ = dbm0.split_off(2);
        assert!(dbm0.write_all("ABCD".as_bytes()).is_err());
    }

    #[test]
    pub fn flush() {
        let dbs0 = DivBufShared::with_capacity(0);
        let mut dbm0 = dbs0.try_mut().unwrap();
        dbm0.write_all("ABCD".as_bytes()).unwrap();
        dbm0.flush().unwrap();
        assert_eq!(&dbm0[..], &[65u8, 66u8, 67u8, 68u8][..])
    }
}