diff --git a/tests/it.rs b/tests/it.rs
deleted file mode 100644
index d18f0a1..0000000
--- a/tests/it.rs
+++ /dev/null
@@ -1,977 +0,0 @@
-mod unsync {
-    use core::{
-        cell::Cell,
-        sync::atomic::{AtomicUsize, Ordering::SeqCst},
-    };
-
-    use once_cell::unsync::{Lazy, OnceCell};
-
-    #[test]
-    fn once_cell() {
-        let c = OnceCell::new();
-        assert!(c.get().is_none());
-        c.get_or_init(|| 92);
-        assert_eq!(c.get(), Some(&92));
-
-        c.get_or_init(|| panic!("Kabom!"));
-        assert_eq!(c.get(), Some(&92));
-    }
-
-    #[test]
-    fn once_cell_with_value() {
-        const CELL: OnceCell<i32> = OnceCell::with_value(12);
-        let cell = CELL;
-        assert_eq!(cell.get(), Some(&12));
-    }
-
-    #[test]
-    fn once_cell_get_mut() {
-        let mut c = OnceCell::new();
-        assert!(c.get_mut().is_none());
-        c.set(90).unwrap();
-        *c.get_mut().unwrap() += 2;
-        assert_eq!(c.get_mut(), Some(&mut 92));
-    }
-
-    #[test]
-    fn once_cell_drop() {
-        static DROP_CNT: AtomicUsize = AtomicUsize::new(0);
-        struct Dropper;
-        impl Drop for Dropper {
-            fn drop(&mut self) {
-                DROP_CNT.fetch_add(1, SeqCst);
-            }
-        }
-
-        let x = OnceCell::new();
-        x.get_or_init(|| Dropper);
-        assert_eq!(DROP_CNT.load(SeqCst), 0);
-        drop(x);
-        assert_eq!(DROP_CNT.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn unsync_once_cell_drop_empty() {
-        let x = OnceCell::<String>::new();
-        drop(x);
-    }
-
-    #[test]
-    fn clone() {
-        let s = OnceCell::new();
-        let c = s.clone();
-        assert!(c.get().is_none());
-
-        s.set("hello".to_string()).unwrap();
-        let c = s.clone();
-        assert_eq!(c.get().map(String::as_str), Some("hello"));
-    }
-
-    #[test]
-    fn from_impl() {
-        assert_eq!(OnceCell::from("value").get(), Some(&"value"));
-        assert_ne!(OnceCell::from("foo").get(), Some(&"bar"));
-    }
-
-    #[test]
-    fn partialeq_impl() {
-        assert!(OnceCell::from("value") == OnceCell::from("value"));
-        assert!(OnceCell::from("foo") != OnceCell::from("bar"));
-
-        assert!(OnceCell::<String>::new() == OnceCell::new());
-        assert!(OnceCell::<String>::new() != OnceCell::from("value".to_owned()));
-    }
-
-    #[test]
-    fn into_inner() {
-        let cell: OnceCell<String> = OnceCell::new();
-        assert_eq!(cell.into_inner(), None);
-        let cell = OnceCell::new();
-        cell.set("hello".to_string()).unwrap();
-        assert_eq!(cell.into_inner(), Some("hello".to_string()));
-    }
-
-    #[test]
-    fn debug_impl() {
-        let cell = OnceCell::new();
-        assert_eq!(format!("{:?}", cell), "OnceCell(Uninit)");
-        cell.set("hello".to_string()).unwrap();
-        assert_eq!(format!("{:?}", cell), "OnceCell(\"hello\")");
-    }
-
-    #[test]
-    fn lazy_new() {
-        let called = Cell::new(0);
-        let x = Lazy::new(|| {
-            called.set(called.get() + 1);
-            92
-        });
-
-        assert_eq!(called.get(), 0);
-
-        let y = *x - 30;
-        assert_eq!(y, 62);
-        assert_eq!(called.get(), 1);
-
-        let y = *x - 30;
-        assert_eq!(y, 62);
-        assert_eq!(called.get(), 1);
-    }
-
-    #[test]
-    fn lazy_deref_mut() {
-        let called = Cell::new(0);
-        let mut x = Lazy::new(|| {
-            called.set(called.get() + 1);
-            92
-        });
-
-        assert_eq!(called.get(), 0);
-
-        let y = *x - 30;
-        assert_eq!(y, 62);
-        assert_eq!(called.get(), 1);
-
-        *x /= 2;
-        assert_eq!(*x, 46);
-        assert_eq!(called.get(), 1);
-    }
-
-    #[test]
-    fn lazy_force_mut() {
-        let called = Cell::new(0);
-        let mut x = Lazy::new(|| {
-            called.set(called.get() + 1);
-            92
-        });
-        assert_eq!(called.get(), 0);
-        let v = Lazy::force_mut(&mut x);
-        assert_eq!(called.get(), 1);
-
-        *v /= 2;
-        assert_eq!(*x, 46);
-        assert_eq!(called.get(), 1);
-    }
-
-    #[test]
-    fn lazy_get_mut() {
-        let called = Cell::new(0);
-        let mut x: Lazy<u32, _> = Lazy::new(|| {
-            called.set(called.get() + 1);
-            92
-        });
-
-        assert_eq!(called.get(), 0);
-        assert_eq!(*x, 92);
-
-        let mut_ref: &mut u32 = Lazy::get_mut(&mut x).unwrap();
-        assert_eq!(called.get(), 1);
-
-        *mut_ref /= 2;
-        assert_eq!(*x, 46);
-        assert_eq!(called.get(), 1);
-    }
-
-    #[test]
-    fn lazy_default() {
-        static CALLED: AtomicUsize = AtomicUsize::new(0);
-
-        struct Foo(u8);
-        impl Default for Foo {
-            fn default() -> Self {
-                CALLED.fetch_add(1, SeqCst);
-                Foo(42)
-            }
-        }
-
-        let lazy: Lazy<std::sync::Mutex<Foo>> = <_>::default();
-
-        assert_eq!(CALLED.load(SeqCst), 0);
-
-        assert_eq!(lazy.lock().unwrap().0, 42);
-        assert_eq!(CALLED.load(SeqCst), 1);
-
-        lazy.lock().unwrap().0 = 21;
-
-        assert_eq!(lazy.lock().unwrap().0, 21);
-        assert_eq!(CALLED.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn lazy_into_value() {
-        let l: Lazy<i32, _> = Lazy::new(|| panic!());
-        assert!(matches!(Lazy::into_value(l), Err(_)));
-        let l = Lazy::new(|| -> i32 { 92 });
-        Lazy::force(&l);
-        assert!(matches!(Lazy::into_value(l), Ok(92)));
-    }
-
-    #[test]
-    #[cfg(feature = "std")]
-    fn lazy_poisoning() {
-        let x: Lazy<String> = Lazy::new(|| panic!("kaboom"));
-        for _ in 0..2 {
-            let res = std::panic::catch_unwind(|| x.len());
-            assert!(res.is_err());
-        }
-    }
-
-    #[test]
-    fn aliasing_in_get() {
-        let x = OnceCell::new();
-        x.set(42).unwrap();
-        let at_x = x.get().unwrap(); // --- (shared) borrow of inner `Option<T>` --+
-        let _ = x.set(27); // <-- temporary (unique) borrow of inner `Option<T>`   |
-        println!("{}", at_x); // <------- up until here ---------------------------+
-    }
-
-    #[test]
-    #[should_panic(expected = "reentrant init")]
-    fn reentrant_init() {
-        let x: OnceCell<Box<i32>> = OnceCell::new();
-        let dangling_ref: Cell<Option<&i32>> = Cell::new(None);
-        x.get_or_init(|| {
-            let r = x.get_or_init(|| Box::new(92));
-            dangling_ref.set(Some(r));
-            Box::new(62)
-        });
-        eprintln!("use after free: {:?}", dangling_ref.get().unwrap());
-    }
-
-    #[test]
-    // https://github.com/rust-lang/rust/issues/34761#issuecomment-256320669
-    fn arrrrrrrrrrrrrrrrrrrrrr() {
-        let cell = OnceCell::new();
-        {
-            let s = String::new();
-            cell.set(&s).unwrap();
-        }
-    }
-}
-
-#[cfg(any(feature = "std", feature = "critical-section"))]
-mod sync {
-    use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};
-
-    #[cfg(feature = "std")]
-    use std::sync::Barrier;
-
-    #[cfg(not(feature = "std"))]
-    use core::cell::Cell;
-
-    use crossbeam_utils::thread::scope;
-
-    use once_cell::sync::{Lazy, OnceCell};
-
-    #[test]
-    fn once_cell() {
-        let c = OnceCell::new();
-        assert!(c.get().is_none());
-        scope(|s| {
-            s.spawn(|_| {
-                c.get_or_init(|| 92);
-                assert_eq!(c.get(), Some(&92));
-            });
-        })
-        .unwrap();
-        c.get_or_init(|| panic!("Kabom!"));
-        assert_eq!(c.get(), Some(&92));
-    }
-
-    #[test]
-    fn once_cell_with_value() {
-        static CELL: OnceCell<i32> = OnceCell::with_value(12);
-        assert_eq!(CELL.get(), Some(&12));
-    }
-
-    #[test]
-    fn once_cell_get_mut() {
-        let mut c = OnceCell::new();
-        assert!(c.get_mut().is_none());
-        c.set(90).unwrap();
-        *c.get_mut().unwrap() += 2;
-        assert_eq!(c.get_mut(), Some(&mut 92));
-    }
-
-    #[test]
-    fn once_cell_get_unchecked() {
-        let c = OnceCell::new();
-        c.set(92).unwrap();
-        unsafe {
-            assert_eq!(c.get_unchecked(), &92);
-        }
-    }
-
-    #[test]
-    fn once_cell_drop() {
-        static DROP_CNT: AtomicUsize = AtomicUsize::new(0);
-        struct Dropper;
-        impl Drop for Dropper {
-            fn drop(&mut self) {
-                DROP_CNT.fetch_add(1, SeqCst);
-            }
-        }
-
-        let x = OnceCell::new();
-        scope(|s| {
-            s.spawn(|_| {
-                x.get_or_init(|| Dropper);
-                assert_eq!(DROP_CNT.load(SeqCst), 0);
-                drop(x);
-            });
-        })
-        .unwrap();
-        assert_eq!(DROP_CNT.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn once_cell_drop_empty() {
-        let x = OnceCell::<String>::new();
-        drop(x);
-    }
-
-    #[test]
-    fn clone() {
-        let s = OnceCell::new();
-        let c = s.clone();
-        assert!(c.get().is_none());
-
-        s.set("hello".to_string()).unwrap();
-        let c = s.clone();
-        assert_eq!(c.get().map(String::as_str), Some("hello"));
-    }
-
-    #[test]
-    fn get_or_try_init() {
-        let cell: OnceCell<String> = OnceCell::new();
-        assert!(cell.get().is_none());
-
-        let res =
-            std::panic::catch_unwind(|| cell.get_or_try_init(|| -> Result<_, ()> { panic!() }));
-        assert!(res.is_err());
-        assert!(cell.get().is_none());
-
-        assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
-
-        assert_eq!(
-            cell.get_or_try_init(|| Ok::<_, ()>("hello".to_string())),
-            Ok(&"hello".to_string())
-        );
-        assert_eq!(cell.get(), Some(&"hello".to_string()));
-    }
-
-    #[cfg(feature = "std")]
-    #[test]
-    fn wait() {
-        let cell: OnceCell<String> = OnceCell::new();
-        scope(|s| {
-            s.spawn(|_| cell.set("hello".to_string()));
-            let greeting = cell.wait();
-            assert_eq!(greeting, "hello")
-        })
-        .unwrap();
-    }
-
-    #[cfg(feature = "std")]
-    #[test]
-    fn get_or_init_stress() {
-        let n_threads = if cfg!(miri) { 30 } else { 1_000 };
-        let n_cells = if cfg!(miri) { 30 } else { 1_000 };
-        let cells: Vec<_> = std::iter::repeat_with(|| (Barrier::new(n_threads), OnceCell::new()))
-            .take(n_cells)
-            .collect();
-        scope(|s| {
-            for t in 0..n_threads {
-                let cells = &cells;
-                s.spawn(move |_| {
-                    for (i, (b, s)) in cells.iter().enumerate() {
-                        b.wait();
-                        let j = if t % 2 == 0 { s.wait() } else { s.get_or_init(|| i) };
-                        assert_eq!(*j, i);
-                    }
-                });
-            }
-        })
-        .unwrap();
-    }
-
-    #[test]
-    fn from_impl() {
-        assert_eq!(OnceCell::from("value").get(), Some(&"value"));
-        assert_ne!(OnceCell::from("foo").get(), Some(&"bar"));
-    }
-
-    #[test]
-    fn partialeq_impl() {
-        assert!(OnceCell::from("value") == OnceCell::from("value"));
-        assert!(OnceCell::from("foo") != OnceCell::from("bar"));
-
-        assert!(OnceCell::<String>::new() == OnceCell::new());
-        assert!(OnceCell::<String>::new() != OnceCell::from("value".to_owned()));
-    }
-
-    #[test]
-    fn into_inner() {
-        let cell: OnceCell<String> = OnceCell::new();
-        assert_eq!(cell.into_inner(), None);
-        let cell = OnceCell::new();
-        cell.set("hello".to_string()).unwrap();
-        assert_eq!(cell.into_inner(), Some("hello".to_string()));
-    }
-
-    #[test]
-    fn debug_impl() {
-        let cell = OnceCell::new();
-        assert_eq!(format!("{:#?}", cell), "OnceCell(Uninit)");
-        cell.set(vec!["hello", "world"]).unwrap();
-        assert_eq!(
-            format!("{:#?}", cell),
-            r#"OnceCell(
-    [
-        "hello",
-        "world",
-    ],
-)"#
-        );
-    }
-
-    #[test]
-    #[cfg_attr(miri, ignore)] // miri doesn't support processes
-    #[cfg(feature = "std")]
-    fn reentrant_init() {
-        let examples_dir = {
-            let mut exe = std::env::current_exe().unwrap();
-            exe.pop();
-            exe.pop();
-            exe.push("examples");
-            exe
-        };
-        let bin = examples_dir
-            .join("reentrant_init_deadlocks")
-            .with_extension(std::env::consts::EXE_EXTENSION);
-        let mut guard = Guard { child: std::process::Command::new(bin).spawn().unwrap() };
-        std::thread::sleep(std::time::Duration::from_secs(2));
-        let status = guard.child.try_wait().unwrap();
-        assert!(status.is_none());
-
-        struct Guard {
-            child: std::process::Child,
-        }
-
-        impl Drop for Guard {
-            fn drop(&mut self) {
-                let _ = self.child.kill();
-            }
-        }
-    }
-
-    #[cfg(not(feature = "std"))]
-    #[test]
-    #[should_panic(expected = "reentrant init")]
-    fn reentrant_init() {
-        let x: OnceCell<Box<i32>> = OnceCell::new();
-        let dangling_ref: Cell<Option<&i32>> = Cell::new(None);
-        x.get_or_init(|| {
-            let r = x.get_or_init(|| Box::new(92));
-            dangling_ref.set(Some(r));
-            Box::new(62)
-        });
-        eprintln!("use after free: {:?}", dangling_ref.get().unwrap());
-    }
-
-    #[test]
-    fn lazy_new() {
-        let called = AtomicUsize::new(0);
-        let x = Lazy::new(|| {
-            called.fetch_add(1, SeqCst);
-            92
-        });
-
-        assert_eq!(called.load(SeqCst), 0);
-
-        scope(|s| {
-            s.spawn(|_| {
-                let y = *x - 30;
-                assert_eq!(y, 62);
-                assert_eq!(called.load(SeqCst), 1);
-            });
-        })
-        .unwrap();
-
-        let y = *x - 30;
-        assert_eq!(y, 62);
-        assert_eq!(called.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn lazy_deref_mut() {
-        let called = AtomicUsize::new(0);
-        let mut x = Lazy::new(|| {
-            called.fetch_add(1, SeqCst);
-            92
-        });
-
-        assert_eq!(called.load(SeqCst), 0);
-
-        let y = *x - 30;
-        assert_eq!(y, 62);
-        assert_eq!(called.load(SeqCst), 1);
-
-        *x /= 2;
-        assert_eq!(*x, 46);
-        assert_eq!(called.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn lazy_default() {
-        static CALLED: AtomicUsize = AtomicUsize::new(0);
-
-        struct Foo(u8);
-        impl Default for Foo {
-            fn default() -> Self {
-                CALLED.fetch_add(1, SeqCst);
-                Foo(42)
-            }
-        }
-
-        let lazy: Lazy<std::sync::Mutex<Foo>> = <_>::default();
-
-        assert_eq!(CALLED.load(SeqCst), 0);
-
-        assert_eq!(lazy.lock().unwrap().0, 42);
-        assert_eq!(CALLED.load(SeqCst), 1);
-
-        lazy.lock().unwrap().0 = 21;
-
-        assert_eq!(lazy.lock().unwrap().0, 21);
-        assert_eq!(CALLED.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn static_lazy() {
-        static XS: Lazy<Vec<i32>> = Lazy::new(|| {
-            let mut xs = Vec::new();
-            xs.push(1);
-            xs.push(2);
-            xs.push(3);
-            xs
-        });
-        scope(|s| {
-            s.spawn(|_| {
-                assert_eq!(&*XS, &vec![1, 2, 3]);
-            });
-        })
-        .unwrap();
-        assert_eq!(&*XS, &vec![1, 2, 3]);
-    }
-
-    #[test]
-    fn static_lazy_via_fn() {
-        fn xs() -> &'static Vec<i32> {
-            static XS: OnceCell<Vec<i32>> = OnceCell::new();
-            XS.get_or_init(|| {
-                let mut xs = Vec::new();
-                xs.push(1);
-                xs.push(2);
-                xs.push(3);
-                xs
-            })
-        }
-        assert_eq!(xs(), &vec![1, 2, 3]);
-    }
-
-    #[test]
-    fn lazy_into_value() {
-        let l: Lazy<i32, _> = Lazy::new(|| panic!());
-        assert!(matches!(Lazy::into_value(l), Err(_)));
-        let l = Lazy::new(|| -> i32 { 92 });
-        Lazy::force(&l);
-        assert!(matches!(Lazy::into_value(l), Ok(92)));
-    }
-
-    #[test]
-    fn lazy_poisoning() {
-        let x: Lazy<String> = Lazy::new(|| panic!("kaboom"));
-        for _ in 0..2 {
-            let res = std::panic::catch_unwind(|| x.len());
-            assert!(res.is_err());
-        }
-    }
-
-    #[test]
-    fn once_cell_is_sync_send() {
-        fn assert_traits<T: Send + Sync>() {}
-        assert_traits::<OnceCell<String>>();
-        assert_traits::<Lazy<String>>();
-    }
-
-    #[test]
-    fn eval_once_macro() {
-        macro_rules! eval_once {
-            (|| -> $ty:ty {
-                $($body:tt)*
-            }) => {{
-                static ONCE_CELL: OnceCell<$ty> = OnceCell::new();
-                fn init() -> $ty {
-                    $($body)*
-                }
-                ONCE_CELL.get_or_init(init)
-            }};
-        }
-
-        let fib: &'static Vec<i32> = eval_once! {
-            || -> Vec<i32> {
-                let mut res = vec![1, 1];
-                for i in 0..10 {
-                    let next = res[i] + res[i + 1];
-                    res.push(next);
-                }
-                res
-            }
-        };
-        assert_eq!(fib[5], 8)
-    }
-
-    #[test]
-    fn once_cell_does_not_leak_partially_constructed_boxes() {
-        let n_tries = if cfg!(miri) { 10 } else { 100 };
-        let n_readers = 10;
-        let n_writers = 3;
-        const MSG: &str = "Hello, World";
-
-        for _ in 0..n_tries {
-            let cell: OnceCell<String> = OnceCell::new();
-            scope(|scope| {
-                for _ in 0..n_readers {
-                    scope.spawn(|_| loop {
-                        if let Some(msg) = cell.get() {
-                            assert_eq!(msg, MSG);
-                            break;
-                        }
-                    });
-                }
-                for _ in 0..n_writers {
-                    let _ = scope.spawn(|_| cell.set(MSG.to_owned()));
-                }
-            })
-            .unwrap()
-        }
-    }
-
-    #[cfg(feature = "std")]
-    #[test]
-    fn get_does_not_block() {
-        let cell = OnceCell::new();
-        let barrier = Barrier::new(2);
-        scope(|scope| {
-            scope.spawn(|_| {
-                cell.get_or_init(|| {
-                    barrier.wait();
-                    barrier.wait();
-                    "hello".to_string()
-                });
-            });
-            barrier.wait();
-            assert_eq!(cell.get(), None);
-            barrier.wait();
-        })
-        .unwrap();
-        assert_eq!(cell.get(), Some(&"hello".to_string()));
-    }
-
-    #[test]
-    // https://github.com/rust-lang/rust/issues/34761#issuecomment-256320669
-    fn arrrrrrrrrrrrrrrrrrrrrr() {
-        let cell = OnceCell::new();
-        {
-            let s = String::new();
-            cell.set(&s).unwrap();
-        }
-    }
-}
-
-#[cfg(feature = "race")]
-mod race {
-    #[cfg(feature = "std")]
-    use std::sync::Barrier;
-    use std::{
-        num::NonZeroUsize,
-        sync::atomic::{AtomicUsize, Ordering::SeqCst},
-    };
-
-    use crossbeam_utils::thread::scope;
-
-    use once_cell::race::{OnceBool, OnceNonZeroUsize};
-
-    #[test]
-    fn once_non_zero_usize_smoke_test() {
-        let cnt = AtomicUsize::new(0);
-        let cell = OnceNonZeroUsize::new();
-        let val = NonZeroUsize::new(92).unwrap();
-        scope(|s| {
-            s.spawn(|_| {
-                assert_eq!(
-                    cell.get_or_init(|| {
-                        cnt.fetch_add(1, SeqCst);
-                        val
-                    }),
-                    val
-                );
-                assert_eq!(cnt.load(SeqCst), 1);
-
-                assert_eq!(
-                    cell.get_or_init(|| {
-                        cnt.fetch_add(1, SeqCst);
-                        val
-                    }),
-                    val
-                );
-                assert_eq!(cnt.load(SeqCst), 1);
-            });
-        })
-        .unwrap();
-        assert_eq!(cell.get(), Some(val));
-        assert_eq!(cnt.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn once_non_zero_usize_set() {
-        let val1 = NonZeroUsize::new(92).unwrap();
-        let val2 = NonZeroUsize::new(62).unwrap();
-
-        let cell = OnceNonZeroUsize::new();
-
-        assert!(cell.set(val1).is_ok());
-        assert_eq!(cell.get(), Some(val1));
-
-        assert!(cell.set(val2).is_err());
-        assert_eq!(cell.get(), Some(val1));
-    }
-
-    #[cfg(feature = "std")]
-    #[test]
-    fn once_non_zero_usize_first_wins() {
-        let val1 = NonZeroUsize::new(92).unwrap();
-        let val2 = NonZeroUsize::new(62).unwrap();
-
-        let cell = OnceNonZeroUsize::new();
-
-        let b1 = Barrier::new(2);
-        let b2 = Barrier::new(2);
-        let b3 = Barrier::new(2);
-        scope(|s| {
-            s.spawn(|_| {
-                let r1 = cell.get_or_init(|| {
-                    b1.wait();
-                    b2.wait();
-                    val1
-                });
-                assert_eq!(r1, val1);
-                b3.wait();
-            });
-            b1.wait();
-            s.spawn(|_| {
-                let r2 = cell.get_or_init(|| {
-                    b2.wait();
-                    b3.wait();
-                    val2
-                });
-                assert_eq!(r2, val1);
-            });
-        })
-        .unwrap();
-
-        assert_eq!(cell.get(), Some(val1));
-    }
-
-    #[test]
-    fn once_bool_smoke_test() {
-        let cnt = AtomicUsize::new(0);
-        let cell = OnceBool::new();
-        scope(|s| {
-            s.spawn(|_| {
-                assert_eq!(
-                    cell.get_or_init(|| {
-                        cnt.fetch_add(1, SeqCst);
-                        false
-                    }),
-                    false
-                );
-                assert_eq!(cnt.load(SeqCst), 1);
-
-                assert_eq!(
-                    cell.get_or_init(|| {
-                        cnt.fetch_add(1, SeqCst);
-                        false
-                    }),
-                    false
-                );
-                assert_eq!(cnt.load(SeqCst), 1);
-            });
-        })
-        .unwrap();
-        assert_eq!(cell.get(), Some(false));
-        assert_eq!(cnt.load(SeqCst), 1);
-    }
-
-    #[test]
-    fn once_bool_set() {
-        let cell = OnceBool::new();
-
-        assert!(cell.set(false).is_ok());
-        assert_eq!(cell.get(), Some(false));
-
-        assert!(cell.set(true).is_err());
-        assert_eq!(cell.get(), Some(false));
-    }
-}
-
-#[cfg(all(feature = "race", feature = "alloc"))]
-mod race_once_box {
-    #[cfg(feature = "std")]
-    use std::sync::Barrier;
-    use std::sync::{
-        atomic::{AtomicUsize, Ordering::SeqCst},
-        Arc,
-    };
-
-    #[cfg(feature = "std")]
-    use crossbeam_utils::thread::scope;
-
-    use once_cell::race::OnceBox;
-
-    #[derive(Default)]
-    struct Heap {
-        total: Arc<AtomicUsize>,
-    }
-
-    #[derive(Debug)]
-    struct Pebble<T> {
-        val: T,
-        total: Arc<AtomicUsize>,
-    }
-
-    impl<T> Drop for Pebble<T> {
-        fn drop(&mut self) {
-            self.total.fetch_sub(1, SeqCst);
-        }
-    }
-
-    impl Heap {
-        fn total(&self) -> usize {
-            self.total.load(SeqCst)
-        }
-        fn new_pebble<T>(&self, val: T) -> Pebble<T> {
-            self.total.fetch_add(1, SeqCst);
-            Pebble { val, total: Arc::clone(&self.total) }
-        }
-    }
-
-    #[cfg(feature = "std")]
-    #[test]
-    fn once_box_smoke_test() {
-        let heap = Heap::default();
-        let global_cnt = AtomicUsize::new(0);
-        let cell = OnceBox::new();
-        let b = Barrier::new(128);
-        scope(|s| {
-            for _ in 0..128 {
-                s.spawn(|_| {
-                    let local_cnt = AtomicUsize::new(0);
-                    cell.get_or_init(|| {
-                        global_cnt.fetch_add(1, SeqCst);
-                        local_cnt.fetch_add(1, SeqCst);
-                        b.wait();
-                        Box::new(heap.new_pebble(()))
-                    });
-                    assert_eq!(local_cnt.load(SeqCst), 1);
-
-                    cell.get_or_init(|| {
-                        global_cnt.fetch_add(1, SeqCst);
-                        local_cnt.fetch_add(1, SeqCst);
-                        Box::new(heap.new_pebble(()))
-                    });
-                    assert_eq!(local_cnt.load(SeqCst), 1);
-                });
-            }
-        })
-        .unwrap();
-        assert!(cell.get().is_some());
-        assert!(global_cnt.load(SeqCst) > 10);
-
-        assert_eq!(heap.total(), 1);
-        drop(cell);
-        assert_eq!(heap.total(), 0);
-    }
-
-    #[test]
-    fn once_box_set() {
-        let heap = Heap::default();
-        let cell = OnceBox::new();
-        assert!(cell.get().is_none());
-
-        assert!(cell.set(Box::new(heap.new_pebble("hello"))).is_ok());
-        assert_eq!(cell.get().unwrap().val, "hello");
-        assert_eq!(heap.total(), 1);
-
-        assert!(cell.set(Box::new(heap.new_pebble("world"))).is_err());
-        assert_eq!(cell.get().unwrap().val, "hello");
-        assert_eq!(heap.total(), 1);
-
-        drop(cell);
-        assert_eq!(heap.total(), 0);
-    }
-
-    #[cfg(feature = "std")]
-    #[test]
-    fn once_box_first_wins() {
-        let cell = OnceBox::new();
-        let val1 = 92;
-        let val2 = 62;
-
-        let b1 = Barrier::new(2);
-        let b2 = Barrier::new(2);
-        let b3 = Barrier::new(2);
-        scope(|s| {
-            s.spawn(|_| {
-                let r1 = cell.get_or_init(|| {
-                    b1.wait();
-                    b2.wait();
-                    Box::new(val1)
-                });
-                assert_eq!(*r1, val1);
-                b3.wait();
-            });
-            b1.wait();
-            s.spawn(|_| {
-                let r2 = cell.get_or_init(|| {
-                    b2.wait();
-                    b3.wait();
-                    Box::new(val2)
-                });
-                assert_eq!(*r2, val1);
-            });
-        })
-        .unwrap();
-
-        assert_eq!(cell.get(), Some(&val1));
-    }
-
-    #[test]
-    fn once_box_reentrant() {
-        let cell = OnceBox::new();
-        let res = cell.get_or_init(|| {
-            cell.get_or_init(|| Box::new("hello".to_string()));
-            Box::new("world".to_string())
-        });
-        assert_eq!(res, "hello");
-    }
-
-    #[test]
-    fn once_box_default() {
-        struct Foo;
-
-        let cell: OnceBox<Foo> = Default::default();
-        assert!(cell.get().is_none());
-    }
-}
diff --git a/tests/it/main.rs b/tests/it/main.rs
new file mode 100644
index 0000000..b8e56cc
--- /dev/null
+++ b/tests/it/main.rs
@@ -0,0 +1,12 @@
+mod unsync_once_cell;
+#[cfg(any(feature = "std", feature = "critical-section"))]
+mod sync_once_cell;
+
+mod unsync_lazy;
+#[cfg(any(feature = "std", feature = "critical-section"))]
+mod sync_lazy;
+
+#[cfg(feature = "race")]
+mod race;
+#[cfg(all(feature = "race", feature = "alloc"))]
+mod race_once_box;
diff --git a/tests/it/race.rs b/tests/it/race.rs
new file mode 100644
index 0000000..6c5e11d
--- /dev/null
+++ b/tests/it/race.rs
@@ -0,0 +1,132 @@
+#[cfg(feature = "std")]
+use std::sync::Barrier;
+use std::{
+    num::NonZeroUsize,
+    sync::atomic::{AtomicUsize, Ordering::SeqCst},
+};
+
+use crossbeam_utils::thread::scope;
+
+use once_cell::race::{OnceBool, OnceNonZeroUsize};
+
+#[test]
+fn once_non_zero_usize_smoke_test() {
+    let cnt = AtomicUsize::new(0);
+    let cell = OnceNonZeroUsize::new();
+    let val = NonZeroUsize::new(92).unwrap();
+    scope(|s| {
+        s.spawn(|_| {
+            assert_eq!(
+                cell.get_or_init(|| {
+                    cnt.fetch_add(1, SeqCst);
+                    val
+                }),
+                val
+            );
+            assert_eq!(cnt.load(SeqCst), 1);
+
+            assert_eq!(
+                cell.get_or_init(|| {
+                    cnt.fetch_add(1, SeqCst);
+                    val
+                }),
+                val
+            );
+            assert_eq!(cnt.load(SeqCst), 1);
+        });
+    })
+    .unwrap();
+    assert_eq!(cell.get(), Some(val));
+    assert_eq!(cnt.load(SeqCst), 1);
+}
+
+#[test]
+fn once_non_zero_usize_set() {
+    let val1 = NonZeroUsize::new(92).unwrap();
+    let val2 = NonZeroUsize::new(62).unwrap();
+
+    let cell = OnceNonZeroUsize::new();
+
+    assert!(cell.set(val1).is_ok());
+    assert_eq!(cell.get(), Some(val1));
+
+    assert!(cell.set(val2).is_err());
+    assert_eq!(cell.get(), Some(val1));
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn once_non_zero_usize_first_wins() {
+    let val1 = NonZeroUsize::new(92).unwrap();
+    let val2 = NonZeroUsize::new(62).unwrap();
+
+    let cell = OnceNonZeroUsize::new();
+
+    let b1 = Barrier::new(2);
+    let b2 = Barrier::new(2);
+    let b3 = Barrier::new(2);
+    scope(|s| {
+        s.spawn(|_| {
+            let r1 = cell.get_or_init(|| {
+                b1.wait();
+                b2.wait();
+                val1
+            });
+            assert_eq!(r1, val1);
+            b3.wait();
+        });
+        b1.wait();
+        s.spawn(|_| {
+            let r2 = cell.get_or_init(|| {
+                b2.wait();
+                b3.wait();
+                val2
+            });
+            assert_eq!(r2, val1);
+        });
+    })
+    .unwrap();
+
+    assert_eq!(cell.get(), Some(val1));
+}
+
+#[test]
+fn once_bool_smoke_test() {
+    let cnt = AtomicUsize::new(0);
+    let cell = OnceBool::new();
+    scope(|s| {
+        s.spawn(|_| {
+            assert_eq!(
+                cell.get_or_init(|| {
+                    cnt.fetch_add(1, SeqCst);
+                    false
+                }),
+                false
+            );
+            assert_eq!(cnt.load(SeqCst), 1);
+
+            assert_eq!(
+                cell.get_or_init(|| {
+                    cnt.fetch_add(1, SeqCst);
+                    false
+                }),
+                false
+            );
+            assert_eq!(cnt.load(SeqCst), 1);
+        });
+    })
+    .unwrap();
+    assert_eq!(cell.get(), Some(false));
+    assert_eq!(cnt.load(SeqCst), 1);
+}
+
+#[test]
+fn once_bool_set() {
+    let cell = OnceBool::new();
+
+    assert!(cell.set(false).is_ok());
+    assert_eq!(cell.get(), Some(false));
+
+    assert!(cell.set(true).is_err());
+    assert_eq!(cell.get(), Some(false));
+}
diff --git a/tests/it/race_once_box.rs b/tests/it/race_once_box.rs
new file mode 100644
index 0000000..2c21b76
--- /dev/null
+++ b/tests/it/race_once_box.rs
@@ -0,0 +1,146 @@
+#[cfg(feature = "std")]
+use std::sync::Barrier;
+use std::sync::{
+    atomic::{AtomicUsize, Ordering::SeqCst},
+    Arc,
+};
+
+#[cfg(feature = "std")]
+use crossbeam_utils::thread::scope;
+
+use once_cell::race::OnceBox;
+
+#[derive(Default)]
+struct Heap {
+    total: Arc<AtomicUsize>,
+}
+
+#[derive(Debug)]
+struct Pebble<T> {
+    val: T,
+    total: Arc<AtomicUsize>,
+}
+
+impl<T> Drop for Pebble<T> {
+    fn drop(&mut self) {
+        self.total.fetch_sub(1, SeqCst);
+    }
+}
+
+impl Heap {
+    fn total(&self) -> usize {
+        self.total.load(SeqCst)
+    }
+    fn new_pebble<T>(&self, val: T) -> Pebble<T> {
+        self.total.fetch_add(1, SeqCst);
+        Pebble { val, total: Arc::clone(&self.total) }
+    }
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn once_box_smoke_test() {
+    let heap = Heap::default();
+    let global_cnt = AtomicUsize::new(0);
+    let cell = OnceBox::new();
+    let b = Barrier::new(128);
+    scope(|s| {
+        for _ in 0..128 {
+            s.spawn(|_| {
+                let local_cnt = AtomicUsize::new(0);
+                cell.get_or_init(|| {
+                    global_cnt.fetch_add(1, SeqCst);
+                    local_cnt.fetch_add(1, SeqCst);
+                    b.wait();
+                    Box::new(heap.new_pebble(()))
+                });
+                assert_eq!(local_cnt.load(SeqCst), 1);
+
+                cell.get_or_init(|| {
+                    global_cnt.fetch_add(1, SeqCst);
+                    local_cnt.fetch_add(1, SeqCst);
+                    Box::new(heap.new_pebble(()))
+                });
+                assert_eq!(local_cnt.load(SeqCst), 1);
+            });
+        }
+    })
+    .unwrap();
+    assert!(cell.get().is_some());
+    assert!(global_cnt.load(SeqCst) > 10);
+
+    assert_eq!(heap.total(), 1);
+    drop(cell);
+    assert_eq!(heap.total(), 0);
+}
+
+#[test]
+fn once_box_set() {
+    let heap = Heap::default();
+    let cell = OnceBox::new();
+    assert!(cell.get().is_none());
+
+    assert!(cell.set(Box::new(heap.new_pebble("hello"))).is_ok());
+    assert_eq!(cell.get().unwrap().val, "hello");
+    assert_eq!(heap.total(), 1);
+
+    assert!(cell.set(Box::new(heap.new_pebble("world"))).is_err());
+    assert_eq!(cell.get().unwrap().val, "hello");
+    assert_eq!(heap.total(), 1);
+
+    drop(cell);
+    assert_eq!(heap.total(), 0);
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn once_box_first_wins() {
+    let cell = OnceBox::new();
+    let val1 = 92;
+    let val2 = 62;
+
+    let b1 = Barrier::new(2);
+    let b2 = Barrier::new(2);
+    let b3 = Barrier::new(2);
+    scope(|s| {
+        s.spawn(|_| {
+            let r1 = cell.get_or_init(|| {
+                b1.wait();
+                b2.wait();
+                Box::new(val1)
+            });
+            assert_eq!(*r1, val1);
+            b3.wait();
+        });
+        b1.wait();
+        s.spawn(|_| {
+            let r2 = cell.get_or_init(|| {
+                b2.wait();
+                b3.wait();
+                Box::new(val2)
+            });
+            assert_eq!(*r2, val1);
+        });
+    })
+    .unwrap();
+
+    assert_eq!(cell.get(), Some(&val1));
+}
+
+#[test]
+fn once_box_reentrant() {
+    let cell = OnceBox::new();
+    let res = cell.get_or_init(|| {
+        cell.get_or_init(|| Box::new("hello".to_string()));
+        Box::new("world".to_string())
+    });
+    assert_eq!(res, "hello");
+}
+
+#[test]
+fn once_box_default() {
+    struct Foo;
+
+    let cell: OnceBox<Foo> = Default::default();
+    assert!(cell.get().is_none());
+}
diff --git a/tests/it/sync_lazy.rs b/tests/it/sync_lazy.rs
new file mode 100644
index 0000000..87c1893
--- /dev/null
+++ b/tests/it/sync_lazy.rs
@@ -0,0 +1,182 @@
+use std::{
+    cell::Cell,
+    sync::atomic::{AtomicUsize, Ordering::SeqCst},
+};
+
+#[cfg(not(feature = "std"))]
+use core::cell::Cell;
+
+use crossbeam_utils::thread::scope;
+
+use once_cell::sync::{Lazy, OnceCell};
+
+#[test]
+fn lazy_new() {
+    let called = AtomicUsize::new(0);
+    let x = Lazy::new(|| {
+        called.fetch_add(1, SeqCst);
+        92
+    });
+
+    assert_eq!(called.load(SeqCst), 0);
+
+    scope(|s| {
+        s.spawn(|_| {
+            let y = *x - 30;
+            assert_eq!(y, 62);
+            assert_eq!(called.load(SeqCst), 1);
+        });
+    })
+    .unwrap();
+
+    let y = *x - 30;
+    assert_eq!(y, 62);
+    assert_eq!(called.load(SeqCst), 1);
+}
+
+#[test]
+fn lazy_deref_mut() {
+    let called = AtomicUsize::new(0);
+    let mut x = Lazy::new(|| {
+        called.fetch_add(1, SeqCst);
+        92
+    });
+
+    assert_eq!(called.load(SeqCst), 0);
+
+    let y = *x - 30;
+    assert_eq!(y, 62);
+    assert_eq!(called.load(SeqCst), 1);
+
+    *x /= 2;
+    assert_eq!(*x, 46);
+    assert_eq!(called.load(SeqCst), 1);
+}
+
+#[test]
+fn lazy_force_mut() {
+    let called = Cell::new(0);
+    let mut x = Lazy::new(|| {
+        called.set(called.get() + 1);
+        92
+    });
+    assert_eq!(called.get(), 0);
+    let v = Lazy::force_mut(&mut x);
+    assert_eq!(called.get(), 1);
+
+    *v /= 2;
+    assert_eq!(*x, 46);
+    assert_eq!(called.get(), 1);
+}
+
+#[test]
+fn lazy_get_mut() {
+    let called = Cell::new(0);
+    let mut x: Lazy<u32, _> = Lazy::new(|| {
+        called.set(called.get() + 1);
+        92
+    });
+
+    assert_eq!(called.get(), 0);
+    assert_eq!(*x, 92);
+
+    let mut_ref: &mut u32 = Lazy::get_mut(&mut x).unwrap();
+    assert_eq!(called.get(), 1);
+
+    *mut_ref /= 2;
+    assert_eq!(*x, 46);
+    assert_eq!(called.get(), 1);
+}
+
+#[test]
+fn lazy_default() {
+    static CALLED: AtomicUsize = AtomicUsize::new(0);
+
+    struct Foo(u8);
+    impl Default for Foo {
+        fn default() -> Self {
+            CALLED.fetch_add(1, SeqCst);
+            Foo(42)
+        }
+    }
+
+    let lazy: Lazy<std::sync::Mutex<Foo>> = <_>::default();
+
+    assert_eq!(CALLED.load(SeqCst), 0);
+
+    assert_eq!(lazy.lock().unwrap().0, 42);
+    assert_eq!(CALLED.load(SeqCst), 1);
+
+    lazy.lock().unwrap().0 = 21;
+
+    assert_eq!(lazy.lock().unwrap().0, 21);
+    assert_eq!(CALLED.load(SeqCst), 1);
+}
+
+#[test]
+fn static_lazy() {
+    static XS: Lazy<Vec<i32>> = Lazy::new(|| {
+        let mut xs = Vec::new();
+        xs.push(1);
+        xs.push(2);
+        xs.push(3);
+        xs
+    });
+    scope(|s| {
+        s.spawn(|_| {
+            assert_eq!(&*XS, &vec![1, 2, 3]);
+        });
+    })
+    .unwrap();
+    assert_eq!(&*XS, &vec![1, 2, 3]);
+}
+
+#[test]
+fn static_lazy_via_fn() {
+    fn xs() -> &'static Vec<i32> {
+        static XS: OnceCell<Vec<i32>> = OnceCell::new();
+        XS.get_or_init(|| {
+            let mut xs = Vec::new();
+            xs.push(1);
+            xs.push(2);
+            xs.push(3);
+            xs
+        })
+    }
+    assert_eq!(xs(), &vec![1, 2, 3]);
+}
+
+#[test]
+fn lazy_into_value() {
+    let l: Lazy<i32, _> = Lazy::new(|| panic!());
+    assert!(matches!(Lazy::into_value(l), Err(_)));
+    let l = Lazy::new(|| -> i32 { 92 });
+    Lazy::force(&l);
+    assert!(matches!(Lazy::into_value(l), Ok(92)));
+}
+
+#[test]
+fn lazy_poisoning() {
+    let x: Lazy<String> = Lazy::new(|| panic!("kaboom"));
+    for _ in 0..2 {
+        let res = std::panic::catch_unwind(|| x.len());
+        assert!(res.is_err());
+    }
+}
+
+#[test]
+// https://github.com/rust-lang/rust/issues/34761#issuecomment-256320669
+fn arrrrrrrrrrrrrrrrrrrrrr() {
+    let lazy: Lazy<&String, _>;
+    {
+        let s = String::new();
+        lazy = Lazy::new(|| &s);
+        _ = *lazy;
+    }
+}
+
+#[test]
+fn lazy_is_sync_send() {
+    fn assert_traits<T: Send + Sync>() {}
+    assert_traits::<Lazy<String>>();
+}
diff --git a/tests/it/sync_once_cell.rs b/tests/it/sync_once_cell.rs
new file mode 100644
index 0000000..9205e6a
--- /dev/null
+++ b/tests/it/sync_once_cell.rs
@@ -0,0 +1,314 @@
+use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};
+
+#[cfg(feature = "std")]
+use std::sync::Barrier;
+
+#[cfg(not(feature = "std"))]
+use core::cell::Cell;
+
+use crossbeam_utils::thread::scope;
+
+use once_cell::sync::{Lazy, OnceCell};
+
+#[test]
+fn once_cell() {
+    let c = OnceCell::new();
+    assert!(c.get().is_none());
+    scope(|s| {
+        s.spawn(|_| {
+            c.get_or_init(|| 92);
+            assert_eq!(c.get(), Some(&92));
+        });
+    })
+    .unwrap();
+    c.get_or_init(|| panic!("Kabom!"));
+    assert_eq!(c.get(), Some(&92));
+}
+
+#[test]
+fn once_cell_with_value() {
+    static CELL: OnceCell<i32> = OnceCell::with_value(12);
+    assert_eq!(CELL.get(), Some(&12));
+}
+
+#[test]
+fn once_cell_get_mut() {
+    let mut c = OnceCell::new();
+    assert!(c.get_mut().is_none());
+    c.set(90).unwrap();
+    *c.get_mut().unwrap() += 2;
+    assert_eq!(c.get_mut(), Some(&mut 92));
+}
+
+#[test]
+fn once_cell_get_unchecked() {
+    let c = OnceCell::new();
+    c.set(92).unwrap();
+    unsafe {
+        assert_eq!(c.get_unchecked(), &92);
+    }
+}
+
+#[test]
+fn once_cell_drop() {
+    static DROP_CNT: AtomicUsize = AtomicUsize::new(0);
+    struct Dropper;
+    impl Drop for Dropper {
+        fn drop(&mut self) {
+            DROP_CNT.fetch_add(1, SeqCst);
+        }
+    }
+
+    let x = OnceCell::new();
+    scope(|s| {
+        s.spawn(|_| {
+            x.get_or_init(|| Dropper);
+            assert_eq!(DROP_CNT.load(SeqCst), 0);
+            drop(x);
+        });
+    })
+    .unwrap();
+    assert_eq!(DROP_CNT.load(SeqCst), 1);
+}
+
+#[test]
+fn once_cell_drop_empty() {
+    let x = OnceCell::<String>::new();
+    drop(x);
+}
+
+#[test]
+fn clone() {
+    let s = OnceCell::new();
+    let c = s.clone();
+    assert!(c.get().is_none());
+
+    s.set("hello".to_string()).unwrap();
+    let c = s.clone();
+    assert_eq!(c.get().map(String::as_str), Some("hello"));
+}
+
+#[test]
+fn get_or_try_init() {
+    let cell: OnceCell<String> = OnceCell::new();
+    assert!(cell.get().is_none());
+
+    let res = std::panic::catch_unwind(|| cell.get_or_try_init(|| -> Result<_, ()> { panic!() }));
+    assert!(res.is_err());
+    assert!(cell.get().is_none());
+
+    assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
+
+    assert_eq!(cell.get_or_try_init(|| Ok::<_, ()>("hello".to_string())), Ok(&"hello".to_string()));
+    assert_eq!(cell.get(), Some(&"hello".to_string()));
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn wait() {
+    let cell: OnceCell<String> = OnceCell::new();
+    scope(|s| {
+        s.spawn(|_| cell.set("hello".to_string()));
+        let greeting = cell.wait();
+        assert_eq!(greeting, "hello")
+    })
+    .unwrap();
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn get_or_init_stress() {
+    let n_threads = if cfg!(miri) { 30 } else { 1_000 };
+    let n_cells = if cfg!(miri) { 30 } else { 1_000 };
+    let cells: Vec<_> = std::iter::repeat_with(|| (Barrier::new(n_threads), OnceCell::new()))
+        .take(n_cells)
+        .collect();
+    scope(|s| {
+        for t in 0..n_threads {
+            let cells = &cells;
+            s.spawn(move |_| {
+                for (i, (b, s)) in cells.iter().enumerate() {
+                    b.wait();
+                    let j = if t % 2 == 0 { s.wait() } else { s.get_or_init(|| i) };
+                    assert_eq!(*j, i);
+                }
+            });
+        }
+    })
+    .unwrap();
+}
+
+#[test]
+fn from_impl() {
+    assert_eq!(OnceCell::from("value").get(), Some(&"value"));
+    assert_ne!(OnceCell::from("foo").get(), Some(&"bar"));
+}
+
+#[test]
+fn partialeq_impl() {
+    assert!(OnceCell::from("value") == OnceCell::from("value"));
+    assert!(OnceCell::from("foo") != OnceCell::from("bar"));
+
+    assert!(OnceCell::<String>::new() == OnceCell::new());
+    assert!(OnceCell::<String>::new() != OnceCell::from("value".to_owned()));
+}
+
+#[test]
+fn into_inner() {
+    let cell: OnceCell<String> = OnceCell::new();
+    assert_eq!(cell.into_inner(), None);
+    let cell = OnceCell::new();
+    cell.set("hello".to_string()).unwrap();
+    assert_eq!(cell.into_inner(), Some("hello".to_string()));
+}
+
+#[test]
+fn debug_impl() {
+    let cell = OnceCell::new();
+    assert_eq!(format!("{:#?}", cell), "OnceCell(Uninit)");
+    cell.set(vec!["hello", "world"]).unwrap();
+    assert_eq!(
+        format!("{:#?}", cell),
+        r#"OnceCell(
+    [
+        "hello",
+        "world",
+    ],
+)"#
+    );
+}
+
+#[test]
+#[cfg_attr(miri, ignore)] // miri doesn't support processes
+#[cfg(feature = "std")]
+fn reentrant_init() {
+    let examples_dir = {
+        let mut exe = std::env::current_exe().unwrap();
+        exe.pop();
+        exe.pop();
+        exe.push("examples");
+        exe
+    };
+    let bin = examples_dir
+        .join("reentrant_init_deadlocks")
+        .with_extension(std::env::consts::EXE_EXTENSION);
+    let mut guard = Guard { child: std::process::Command::new(bin).spawn().unwrap() };
+    std::thread::sleep(std::time::Duration::from_secs(2));
+    let status = guard.child.try_wait().unwrap();
+    assert!(status.is_none());
+
+    struct Guard {
+        child: std::process::Child,
+    }
+
+    impl Drop for Guard {
+        fn drop(&mut self) {
+            let _ = self.child.kill();
+        }
+    }
+}
+
+#[cfg(not(feature = "std"))]
+#[test]
+#[should_panic(expected = "reentrant init")]
+fn reentrant_init() {
+    let x: OnceCell<Box<i32>> = OnceCell::new();
+    let dangling_ref: Cell<Option<&i32>> = Cell::new(None);
+    x.get_or_init(|| {
+        let r = x.get_or_init(|| Box::new(92));
+        dangling_ref.set(Some(r));
+        Box::new(62)
+    });
+    eprintln!("use after free: {:?}", dangling_ref.get().unwrap());
+}
+
+#[test]
+fn eval_once_macro() {
+    macro_rules! eval_once {
+        (|| -> $ty:ty {
+            $($body:tt)*
+        }) => {{
+            static ONCE_CELL: OnceCell<$ty> = OnceCell::new();
+            fn init() -> $ty {
+                $($body)*
+            }
+            ONCE_CELL.get_or_init(init)
+        }};
+    }
+
+    let fib: &'static Vec<i32> = eval_once! {
+        || -> Vec<i32> {
+            let mut res = vec![1, 1];
+            for i in 0..10 {
+                let next = res[i] + res[i + 1];
+                res.push(next);
+            }
+            res
+        }
+    };
+    assert_eq!(fib[5], 8)
+}
+
+#[test]
+fn once_cell_does_not_leak_partially_constructed_boxes() {
+    let n_tries = if cfg!(miri) { 10 } else { 100 };
+    let n_readers = 10;
+    let n_writers = 3;
+    const MSG: &str = "Hello, World";
+
+    for _ in 0..n_tries {
+        let cell: OnceCell<String> = OnceCell::new();
+        scope(|scope| {
+            for _ in 0..n_readers {
+                scope.spawn(|_| loop {
+                    if let Some(msg) = cell.get() {
+                        assert_eq!(msg, MSG);
+                        break;
+                    }
+                });
+            }
+            for _ in 0..n_writers {
+                let _ = scope.spawn(|_| cell.set(MSG.to_owned()));
+            }
+        })
+        .unwrap()
+    }
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn get_does_not_block() {
+    let cell = OnceCell::new();
+    let barrier = Barrier::new(2);
+    scope(|scope| {
+        scope.spawn(|_| {
+            cell.get_or_init(|| {
+                barrier.wait();
+                barrier.wait();
+                "hello".to_string()
+            });
+        });
+        barrier.wait();
+        assert_eq!(cell.get(), None);
+        barrier.wait();
+    })
+    .unwrap();
+    assert_eq!(cell.get(), Some(&"hello".to_string()));
+}
+
+#[test]
+// https://github.com/rust-lang/rust/issues/34761#issuecomment-256320669
+fn arrrrrrrrrrrrrrrrrrrrrr() {
+    let cell = OnceCell::new();
+    {
+        let s = String::new();
+        cell.set(&s).unwrap();
+    }
+}
+
+#[test]
+fn once_cell_is_sync_send() {
+    fn assert_traits<T: Send + Sync>() {}
+    assert_traits::<OnceCell<String>>();
+    assert_traits::<Lazy<String>>();
+}
diff --git a/tests/it/unsync_lazy.rs b/tests/it/unsync_lazy.rs
new file mode 100644
index 0000000..0c308ca
--- /dev/null
+++ b/tests/it/unsync_lazy.rs
@@ -0,0 +1,134 @@
+use core::{
+    cell::Cell,
+    sync::atomic::{AtomicUsize, Ordering::SeqCst},
+};
+
+use once_cell::unsync::Lazy;
+
+#[test]
+fn lazy_new() {
+    let called = Cell::new(0);
+    let x = Lazy::new(|| {
+        called.set(called.get() + 1);
+        92
+    });
+
+    assert_eq!(called.get(), 0);
+
+    let y = *x - 30;
+    assert_eq!(y, 62);
+    assert_eq!(called.get(), 1);
+
+    let y = *x - 30;
+    assert_eq!(y, 62);
+    assert_eq!(called.get(), 1);
+}
+
+#[test]
+fn lazy_deref_mut() {
+    let called = Cell::new(0);
+    let mut x = Lazy::new(|| {
+        called.set(called.get() + 1);
+        92
+    });
+
+    assert_eq!(called.get(), 0);
+
+    let y = *x - 30;
+    assert_eq!(y, 62);
+    assert_eq!(called.get(), 1);
+
+    *x /= 2;
+    assert_eq!(*x, 46);
+    assert_eq!(called.get(), 1);
+}
+
+#[test]
+fn lazy_force_mut() {
+    let called = Cell::new(0);
+    let mut x = Lazy::new(|| {
+        called.set(called.get() + 1);
+        92
+    });
+    assert_eq!(called.get(), 0);
+    let v = Lazy::force_mut(&mut x);
+    assert_eq!(called.get(), 1);
+
+    *v /= 2;
+    assert_eq!(*x, 46);
+    assert_eq!(called.get(), 1);
+}
+
+#[test]
+fn lazy_get_mut() {
+    let called = Cell::new(0);
+    let mut x: Lazy<u32, _> = Lazy::new(|| {
+        called.set(called.get() + 1);
+        92
+    });
+
+    assert_eq!(called.get(), 0);
+    assert_eq!(*x, 92);
+
+    let mut_ref: &mut u32 = Lazy::get_mut(&mut x).unwrap();
+    assert_eq!(called.get(), 1);
+
+    *mut_ref /= 2;
+    assert_eq!(*x, 46);
+    assert_eq!(called.get(), 1);
+}
+
+#[test]
+fn lazy_default() {
+    static CALLED: AtomicUsize = AtomicUsize::new(0);
+
+    struct Foo(u8);
+    impl Default for Foo {
+        fn default() -> Self {
+            CALLED.fetch_add(1, SeqCst);
+            Foo(42)
+        }
+    }
+
+    let lazy: Lazy<std::sync::Mutex<Foo>> = <_>::default();
+
+    assert_eq!(CALLED.load(SeqCst), 0);
+
+    assert_eq!(lazy.lock().unwrap().0, 42);
+    assert_eq!(CALLED.load(SeqCst), 1);
+
+    lazy.lock().unwrap().0 = 21;
+
+    assert_eq!(lazy.lock().unwrap().0, 21);
+    assert_eq!(CALLED.load(SeqCst), 1);
+}
+
+#[test]
+fn lazy_into_value() {
+    let l: Lazy<i32, _> = Lazy::new(|| panic!());
+    assert!(matches!(Lazy::into_value(l), Err(_)));
+    let l = Lazy::new(|| -> i32 { 92 });
+    Lazy::force(&l);
+    assert!(matches!(Lazy::into_value(l), Ok(92)));
+}
+
+#[test]
+#[cfg(feature = "std")]
+fn lazy_poisoning() {
+    let x: Lazy<String> = Lazy::new(|| panic!("kaboom"));
+    for _ in 0..2 {
+        let res = std::panic::catch_unwind(|| x.len());
+        assert!(res.is_err());
+    }
+}
+
+#[test]
+// https://github.com/rust-lang/rust/issues/34761#issuecomment-256320669
+fn arrrrrrrrrrrrrrrrrrrrrr() {
+    let lazy: Lazy<&String, _>;
+    {
+        let s = String::new();
+        lazy = Lazy::new(|| &s);
+        _ = *lazy;
+    }
+}
diff --git a/tests/it/unsync_once_cell.rs b/tests/it/unsync_once_cell.rs
new file mode 100644
index 0000000..124cc3e
--- /dev/null
+++ b/tests/it/unsync_once_cell.rs
@@ -0,0 +1,154 @@
+use core::{
+    cell::Cell,
+    sync::atomic::{AtomicUsize, Ordering::SeqCst},
+};
+
+use once_cell::unsync::OnceCell;
+
+#[test]
+fn once_cell() {
+    let c = OnceCell::new();
+    assert!(c.get().is_none());
+    c.get_or_init(|| 92);
+    assert_eq!(c.get(), Some(&92));
+
+    c.get_or_init(|| panic!("Kabom!"));
+    assert_eq!(c.get(), Some(&92));
+}
+
+#[test]
+fn once_cell_with_value() {
+    const CELL: OnceCell<i32> = OnceCell::with_value(12);
+    let cell = CELL;
+    assert_eq!(cell.get(), Some(&12));
+}
+
+#[test]
+fn once_cell_get_mut() {
+    let mut c = OnceCell::new();
+    assert!(c.get_mut().is_none());
+    c.set(90).unwrap();
+    *c.get_mut().unwrap() += 2;
+    assert_eq!(c.get_mut(), Some(&mut 92));
+}
+
+#[test]
+fn once_cell_drop() {
+    static DROP_CNT: AtomicUsize = AtomicUsize::new(0);
+    struct Dropper;
+    impl Drop for Dropper {
+        fn drop(&mut self) {
+            DROP_CNT.fetch_add(1, SeqCst);
+        }
+    }
+
+    let x = OnceCell::new();
+    x.get_or_init(|| Dropper);
+    assert_eq!(DROP_CNT.load(SeqCst), 0);
+    drop(x);
+    assert_eq!(DROP_CNT.load(SeqCst), 1);
+}
+
+#[test]
+fn once_cell_drop_empty() {
+    let x = OnceCell::<String>::new();
+    drop(x);
+}
+
+#[test]
+fn clone() {
+    let s = OnceCell::new();
+    let c = s.clone();
+    assert!(c.get().is_none());
+
+    s.set("hello".to_string()).unwrap();
+    let c = s.clone();
+    assert_eq!(c.get().map(String::as_str), Some("hello"));
+}
+
+#[test]
+fn get_or_try_init() {
+    let cell: OnceCell<String> = OnceCell::new();
+    assert!(cell.get().is_none());
+
+    let res = std::panic::catch_unwind(|| cell.get_or_try_init(|| -> Result<_, ()> { panic!() }));
+    assert!(res.is_err());
+    assert!(cell.get().is_none());
+
+    assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
+
+    assert_eq!(cell.get_or_try_init(|| Ok::<_, ()>("hello".to_string())), Ok(&"hello".to_string()));
+    assert_eq!(cell.get(), Some(&"hello".to_string()));
+}
+
+#[test]
+fn from_impl() {
+    assert_eq!(OnceCell::from("value").get(), Some(&"value"));
+    assert_ne!(OnceCell::from("foo").get(), Some(&"bar"));
+}
+
+#[test]
+fn partialeq_impl() {
+    assert!(OnceCell::from("value") == OnceCell::from("value"));
+    assert!(OnceCell::from("foo") != OnceCell::from("bar"));
+
+    assert!(OnceCell::<String>::new() == OnceCell::new());
+    assert!(OnceCell::<String>::new() != OnceCell::from("value".to_owned()));
+}
+
+#[test]
+fn into_inner() {
+    let cell: OnceCell<String> = OnceCell::new();
+    assert_eq!(cell.into_inner(), None);
+    let cell = OnceCell::new();
+    cell.set("hello".to_string()).unwrap();
+    assert_eq!(cell.into_inner(), Some("hello".to_string()));
+}
+
+#[test]
+fn debug_impl() {
+    let cell = OnceCell::new();
+    assert_eq!(format!("{:#?}", cell), "OnceCell(Uninit)");
+    cell.set(vec!["hello", "world"]).unwrap();
+    assert_eq!(
+        format!("{:#?}", cell),
+        r#"OnceCell(
+    [
+        "hello",
+        "world",
+    ],
+)"#
+    );
+}
+
+#[test]
+#[should_panic(expected = "reentrant init")]
+fn reentrant_init() {
+    let x: OnceCell<Box<i32>> = OnceCell::new();
+    let dangling_ref: Cell<Option<&i32>> = Cell::new(None);
+    x.get_or_init(|| {
+        let r = x.get_or_init(|| Box::new(92));
+        dangling_ref.set(Some(r));
+        Box::new(62)
+    });
+    eprintln!("use after free: {:?}", dangling_ref.get().unwrap());
+}
+
+#[test]
+fn aliasing_in_get() {
+    let x = OnceCell::new();
+    x.set(42).unwrap();
+    let at_x = x.get().unwrap(); // --- (shared) borrow of inner `Option<T>` --+
+    let _ = x.set(27); // <-- temporary (unique) borrow of inner `Option<T>`   |
+    println!("{}", at_x); // <------- up until here ---------------------------+
+}
+
+#[test]
+// https://github.com/rust-lang/rust/issues/34761#issuecomment-256320669
+fn arrrrrrrrrrrrrrrrrrrrrr() {
+    let cell = OnceCell::new();
+    {
+        let s = String::new();
+        cell.set(&s).unwrap();
+    }
+}