Copy tests from the thread_local crate

Some behavioral modifications had to be made,
but after I got it to compile, all the tests passed!
I am rather surprised at this, but I guess that's the benefit of using safe code ;)

Code is under the same license, so it should be fine.

Author: Techcable

tests/from_thread_local.rs

@@ -0,0 +1,115 @@
+//! Tests copied from the [`thread_local`] crate.
+//!
+//! The following behavioral changes have been made:
+//! - Removed use of unsupported `clear` method (`same_thread` test)
+//! - Iteration should not expect to see values from dead value (`iter` test)
+//! - Remove `RefCell<String>` from test_sync - Currently `!Sync` types are unsupported
+use std::sync::Arc;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering::Relaxed;
+use std::thread;
+
+use dropping_thread_local::DroppingThreadLocal;
+
+fn make_create() -> Arc<dyn Fn() -> usize + Send + Sync> {
+    let count = AtomicUsize::new(0);
+    Arc::new(move || count.fetch_add(1, Relaxed))
+}
+
+#[test]
+fn same_thread() {
+    let create = make_create();
+    let tls = DroppingThreadLocal::new();
+    assert_eq!(None, tls.get());
+    assert_eq!("DroppingThreadLocal { local_data: None }", format!("{:?}", &tls));
+    assert_eq!(0, *tls.get_or_init(|| create()));
+    assert_eq!(Some(&0), tls.get().as_deref());
+    assert_eq!(0, *tls.get_or_init(|| create()));
+    assert_eq!(Some(&0), tls.get().as_deref());
+    assert_eq!(0, *tls.get_or_init(|| create()));
+    assert_eq!(Some(&0), tls.get().as_deref());
+    assert_eq!("DroppingThreadLocal { local_data: Some(0) }", format!("{:?}", &tls));
+    // DroppingThreadLocal::clear is currently not implemented
+    #[cfg(any())]
+    {
+        tls.clear();
+        assert_eq!(None, tls.get());
+    }
+}
+
+#[test]
+fn different_thread() {
+    let create = make_create();
+    let tls = Arc::new(DroppingThreadLocal::new());
+    assert_eq!(None, tls.get());
+    assert_eq!(0, *tls.get_or_init(|| create()));
+    assert_eq!(Some(&0), tls.get().as_deref());
+
+    let tls2 = tls.clone();
+    let create2 = create.clone();
+    thread::spawn(move || {
+        assert_eq!(None, tls2.get());
+        assert_eq!(1, *tls2.get_or_init(|| create2()));
+        assert_eq!(Some(&1), tls2.get().as_deref());
+    })
+    .join()
+    .unwrap();
+
+    assert_eq!(Some(&0), tls.get().as_deref());
+    assert_eq!(0, *tls.get_or_init(|| create()));
+}
+
+#[test]
+fn iter() {
+    let tls = Arc::new(DroppingThreadLocal::new());
+    tls.get_or_init(|| Box::new(1));
+
+    let tls2 = tls.clone();
+    thread::spawn(move || {
+        tls2.get_or_init(|| Box::new(2));
+        let tls3 = tls2.clone();
+        thread::spawn(move || {
+            tls3.get_or_init(|| Box::new(3));
+        })
+        .join()
+        .unwrap();
+        drop(tls2);
+    })
+    .join()
+    .unwrap();
+
+    let tls = Arc::try_unwrap(tls).unwrap();
+
+    let mut v = tls.snapshot_iter().map(|x| **x).collect::<Vec<i32>>();
+    v.sort_unstable();
+    // unlike the thread_local crate, dead values should be dropped b now
+    assert_eq!(v, vec![1])
+}
+
+#[test]
+fn test_drop_local() {
+    let local = DroppingThreadLocal::new();
+    struct Dropped(Arc<AtomicUsize>);
+    impl Drop for Dropped {
+        fn drop(&mut self) {
+            self.0.fetch_add(1, Relaxed);
+        }
+    }
+
+    let dropped = Arc::new(AtomicUsize::new(0));
+    local.get_or_init(|| Dropped(dropped.clone()));
+    assert_eq!(dropped.load(Relaxed), 0);
+    drop(local);
+    assert_eq!(dropped.load(Relaxed), 1);
+}
+
+#[test]
+fn is_sync() {
+    fn foo<T: Sync>() {}
+    foo::<DroppingThreadLocal<String>>();
+    // currently, DroppingThreadLocal requires T: Sync
+    #[cfg(any())]
+    {
+        foo::<DroppingThreadLocal<RefCell<String>>>();
+    }
+}