15 files changed, 678 insertions, 240 deletions

diff --git a/src/libcore/tests/array.rs b/src/libcore/tests/array.rs
index 6af031dee58..6278d5e23e0 100644
--- a/src/libcore/tests/array.rs
+++ b/src/libcore/tests/array.rs
@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 use core::array::FixedSizeArray;
+use core::convert::TryFrom;
 
 #[test]
 fn fixed_size_array() {
@@ -26,3 +27,25 @@ fn fixed_size_array() {
     assert_eq!(FixedSizeArray::as_mut_slice(&mut empty_array).len(), 0);
     assert_eq!(FixedSizeArray::as_mut_slice(&mut empty_zero_sized).len(), 0);
 }
+
+#[test]
+fn array_try_from() {
+    macro_rules! test {
+        ($($N:expr)+) => {
+            $({
+                type Array = [u8; $N];
+                let array: Array = [0; $N];
+                let slice: &[u8] = &array[..];
+
+                let result = <&Array>::try_from(slice);
+                assert_eq!(&array, result.unwrap());
+            })+
+        }
+    }
+    test! {
+         0  1  2  3  4  5  6  7  8  9
+        10 11 12 13 14 15 16 17 18 19
+        20 21 22 23 24 25 26 27 28 29
+        30 31 32
+    }
+}
diff --git a/src/libcore/tests/char.rs b/src/libcore/tests/char.rs
index 7c3b90c8153..4e10ceac878 100644
--- a/src/libcore/tests/char.rs
+++ b/src/libcore/tests/char.rs
@@ -32,7 +32,6 @@ fn test_convert() {
 #[test]
 fn test_from_str() {
     assert_eq!(char::from_str("a").unwrap(), 'a');
-    assert_eq!(char::try_from("a").unwrap(), 'a');
     assert_eq!(char::from_str("\0").unwrap(), '\0');
     assert_eq!(char::from_str("\u{D7FF}").unwrap(), '\u{d7FF}');
     assert!(char::from_str("").is_err());
diff --git a/src/libcore/tests/hash/mod.rs b/src/libcore/tests/hash/mod.rs
index e8ea6044f5f..8716421b424 100644
--- a/src/libcore/tests/hash/mod.rs
+++ b/src/libcore/tests/hash/mod.rs
@@ -12,6 +12,7 @@ mod sip;
 
 use std::hash::{Hash, Hasher};
 use std::default::Default;
+use std::rc::Rc;
 
 struct MyHasher {
     hash: u64,
@@ -64,18 +65,28 @@ fn test_writer_hasher() {
     assert_eq!(hash(& s), 97 + 0xFF);
     let s: Box<str> = String::from("a").into_boxed_str();
     assert_eq!(hash(& s), 97 + 0xFF);
+    let s: Rc<&str> = Rc::new("a");
+    assert_eq!(hash(&s), 97 + 0xFF);
     let cs: &[u8] = &[1, 2, 3];
     assert_eq!(hash(& cs), 9);
     let cs: Box<[u8]> = Box::new([1, 2, 3]);
     assert_eq!(hash(& cs), 9);
-
-    // FIXME (#18248) Add tests for hashing Rc<str> and Rc<[T]>
+    let cs: Rc<[u8]> = Rc::new([1, 2, 3]);
+    assert_eq!(hash(& cs), 9);
 
     let ptr = 5_usize as *const i32;
     assert_eq!(hash(&ptr), 5);
 
     let ptr = 5_usize as *mut i32;
     assert_eq!(hash(&ptr), 5);
+
+    let cs: &mut [u8] = &mut [1, 2, 3];
+    let ptr = cs.as_ptr();
+    let slice_ptr = cs as *const [u8];
+    assert_eq!(hash(&slice_ptr), hash(&ptr) + cs.len() as u64);
+
+    let slice_ptr = cs as *mut [u8];
+    assert_eq!(hash(&slice_ptr), hash(&ptr) + cs.len() as u64);
 }
 
 struct Custom { hash: u64 }
diff --git a/src/libcore/tests/hash/sip.rs b/src/libcore/tests/hash/sip.rs
index 4a9657e0340..c6dd41798f2 100644
--- a/src/libcore/tests/hash/sip.rs
+++ b/src/libcore/tests/hash/sip.rs
@@ -243,24 +243,22 @@ fn test_siphash_2_4() {
         t += 1;
     }
 }
-#[test] #[cfg(target_arch = "arm")]
+
+#[test]
+#[cfg(target_pointer_width = "32")]
 fn test_hash_usize() {
     let val = 0xdeadbeef_deadbeef_u64;
     assert!(hash(&(val as u64)) != hash(&(val as usize)));
     assert_eq!(hash(&(val as u32)), hash(&(val as usize)));
 }
-#[test] #[cfg(target_arch = "x86_64")]
+
+#[test]
+#[cfg(target_pointer_width = "64")]
 fn test_hash_usize() {
     let val = 0xdeadbeef_deadbeef_u64;
     assert_eq!(hash(&(val as u64)), hash(&(val as usize)));
     assert!(hash(&(val as u32)) != hash(&(val as usize)));
 }
-#[test] #[cfg(target_arch = "x86")]
-fn test_hash_usize() {
-    let val = 0xdeadbeef_deadbeef_u64;
-    assert!(hash(&(val as u64)) != hash(&(val as usize)));
-    assert_eq!(hash(&(val as u32)), hash(&(val as usize)));
-}
 
 #[test]
 fn test_hash_idempotent() {
diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index 3c4ea974fc9..5cac5b26d88 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -249,6 +249,25 @@ fn test_filter_map() {
 }
 
 #[test]
+fn test_filter_map_fold() {
+    let xs = [0, 1, 2, 3, 4, 5, 6, 7, 8];
+    let ys = [0*0, 2*2, 4*4, 6*6, 8*8];
+    let it = xs.iter().filter_map(|&x| if x % 2 == 0 { Some(x*x) } else { None });
+    let i = it.fold(0, |i, x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let it = xs.iter().filter_map(|&x| if x % 2 == 0 { Some(x*x) } else { None });
+    let i = it.rfold(ys.len(), |i, x| {
+        assert_eq!(x, ys[i - 1]);
+        i - 1
+    });
+    assert_eq!(i, 0);
+}
+
+#[test]
 fn test_iterator_enumerate() {
     let xs = [0, 1, 2, 3, 4, 5];
     let it = xs.iter().enumerate();
@@ -282,7 +301,31 @@ fn test_iterator_enumerate_nth() {
 #[test]
 fn test_iterator_enumerate_count() {
     let xs = [0, 1, 2, 3, 4, 5];
-    assert_eq!(xs.iter().count(), 6);
+    assert_eq!(xs.iter().enumerate().count(), 6);
+}
+
+#[test]
+fn test_iterator_enumerate_fold() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let mut it = xs.iter().enumerate();
+    // steal a couple to get an interesting offset
+    assert_eq!(it.next(), Some((0, &0)));
+    assert_eq!(it.next(), Some((1, &1)));
+    let i = it.fold(2, |i, (j, &x)| {
+        assert_eq!(i, j);
+        assert_eq!(x, xs[j]);
+        i + 1
+    });
+    assert_eq!(i, xs.len());
+
+    let mut it = xs.iter().enumerate();
+    assert_eq!(it.next(), Some((0, &0)));
+    let i = it.rfold(xs.len() - 1, |i, (j, &x)| {
+        assert_eq!(i, j);
+        assert_eq!(x, xs[j]);
+        i - 1
+    });
+    assert_eq!(i, 0);
 }
 
 #[test]
@@ -292,6 +335,25 @@ fn test_iterator_filter_count() {
 }
 
 #[test]
+fn test_iterator_filter_fold() {
+    let xs = [0, 1, 2, 3, 4, 5, 6, 7, 8];
+    let ys = [0, 2, 4, 6, 8];
+    let it = xs.iter().filter(|&&x| x % 2 == 0);
+    let i = it.fold(0, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let it = xs.iter().filter(|&&x| x % 2 == 0);
+    let i = it.rfold(ys.len(), |i, &x| {
+        assert_eq!(x, ys[i - 1]);
+        i - 1
+    });
+    assert_eq!(i, 0);
+}
+
+#[test]
 fn test_iterator_peekable() {
     let xs = vec![0, 1, 2, 3, 4, 5];
     let mut it = xs.iter().cloned().peekable();
@@ -381,6 +443,18 @@ fn test_iterator_peekable_last() {
     assert_eq!(it.last(), None);
 }
 
+#[test]
+fn test_iterator_peekable_fold() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let mut it = xs.iter().peekable();
+    assert_eq!(it.peek(), Some(&&0));
+    let i = it.fold(0, |i, &x| {
+        assert_eq!(x, xs[i]);
+        i + 1
+    });
+    assert_eq!(i, xs.len());
+}
+
 /// This is an iterator that follows the Iterator contract,
 /// but it is not fused. After having returned None once, it will start
 /// producing elements if .next() is called again.
@@ -471,6 +545,26 @@ fn test_iterator_skip_while() {
 }
 
 #[test]
+fn test_iterator_skip_while_fold() {
+    let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19];
+    let ys = [15, 16, 17, 19];
+    let it = xs.iter().skip_while(|&x| *x < 15);
+    let i = it.fold(0, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let mut it = xs.iter().skip_while(|&x| *x < 15);
+    assert_eq!(it.next(), Some(&ys[0])); // process skips before folding
+    let i = it.fold(1, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+}
+
+#[test]
 fn test_iterator_skip() {
     let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19, 20, 30];
     let ys = [13, 15, 16, 17, 19, 20, 30];
@@ -567,6 +661,45 @@ fn test_iterator_skip_last() {
 }
 
 #[test]
+fn test_iterator_skip_fold() {
+    let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19, 20, 30];
+    let ys = [13, 15, 16, 17, 19, 20, 30];
+
+    let it = xs.iter().skip(5);
+    let i = it.fold(0, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let mut it = xs.iter().skip(5);
+    assert_eq!(it.next(), Some(&ys[0])); // process skips before folding
+    let i = it.fold(1, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let it = xs.iter().skip(5);
+    let i = it.rfold(ys.len(), |i, &x| {
+        let i = i - 1;
+        assert_eq!(x, ys[i]);
+        i
+    });
+    assert_eq!(i, 0);
+
+    let mut it = xs.iter().skip(5);
+    assert_eq!(it.next(), Some(&ys[0])); // process skips before folding
+    let i = it.rfold(ys.len(), |i, &x| {
+        let i = i - 1;
+        assert_eq!(x, ys[i]);
+        i
+    });
+    assert_eq!(i, 1);
+
+}
+
+#[test]
 fn test_iterator_take() {
     let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19];
     let ys = [0, 1, 2, 3, 5];
@@ -661,13 +794,22 @@ fn test_iterator_flat_map_fold() {
     let xs = [0, 3, 6];
     let ys = [1, 2, 3, 4, 5, 6, 7];
     let mut it = xs.iter().flat_map(|&x| x..x+3);
-    it.next();
-    it.next_back();
+    assert_eq!(it.next(), Some(0));
+    assert_eq!(it.next_back(), Some(8));
     let i = it.fold(0, |i, x| {
         assert_eq!(x, ys[i]);
         i + 1
     });
     assert_eq!(i, ys.len());
+
+    let mut it = xs.iter().flat_map(|&x| x..x+3);
+    assert_eq!(it.next(), Some(0));
+    assert_eq!(it.next_back(), Some(8));
+    let i = it.rfold(ys.len(), |i, x| {
+        assert_eq!(x, ys[i - 1]);
+        i - 1
+    });
+    assert_eq!(i, 0);
 }
 
 #[test]
@@ -685,6 +827,32 @@ fn test_inspect() {
 }
 
 #[test]
+fn test_inspect_fold() {
+    let xs = [1, 2, 3, 4];
+    let mut n = 0;
+    {
+        let it = xs.iter().inspect(|_| n += 1);
+        let i = it.fold(0, |i, &x| {
+            assert_eq!(x, xs[i]);
+            i + 1
+        });
+        assert_eq!(i, xs.len());
+    }
+    assert_eq!(n, xs.len());
+
+    let mut n = 0;
+    {
+        let it = xs.iter().inspect(|_| n += 1);
+        let i = it.rfold(xs.len(), |i, &x| {
+            assert_eq!(x, xs[i - 1]);
+            i - 1
+        });
+        assert_eq!(i, 0);
+    }
+    assert_eq!(n, xs.len());
+}
+
+#[test]
 fn test_cycle() {
     let cycle_len = 3;
     let it = (0..).step_by(1).take(cycle_len).cycle();
@@ -1242,6 +1410,31 @@ fn test_fuse_count() {
 }
 
 #[test]
+fn test_fuse_fold() {
+    let xs = [0, 1, 2];
+    let it = xs.iter(); // `FusedIterator`
+    let i = it.fuse().fold(0, |i, &x| {
+        assert_eq!(x, xs[i]);
+        i + 1
+    });
+    assert_eq!(i, xs.len());
+
+    let it = xs.iter(); // `FusedIterator`
+    let i = it.fuse().rfold(xs.len(), |i, &x| {
+        assert_eq!(x, xs[i - 1]);
+        i - 1
+    });
+    assert_eq!(i, 0);
+
+    let it = xs.iter().scan((), |_, &x| Some(x)); // `!FusedIterator`
+    let i = it.fuse().fold(0, |i, x| {
+        assert_eq!(x, xs[i]);
+        i + 1
+    });
+    assert_eq!(i, xs.len());
+}
+
+#[test]
 fn test_once() {
     let mut it = once(42);
     assert_eq!(it.next(), Some(42));
@@ -1304,3 +1497,207 @@ fn test_step_replace_no_between() {
     assert_eq!(x, 1);
     assert_eq!(y, 5);
 }
+
+#[test]
+fn test_rev_try_folds() {
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!((1..10).rev().try_fold(7, f), (1..10).try_rfold(7, f));
+    assert_eq!((1..10).rev().try_rfold(7, f), (1..10).try_fold(7, f));
+
+    let a = [10, 20, 30, 40, 100, 60, 70, 80, 90];
+    let mut iter = a.iter().rev();
+    assert_eq!(iter.try_fold(0_i8, |acc, &x| acc.checked_add(x)), None);
+    assert_eq!(iter.next(), Some(&70));
+    let mut iter = a.iter().rev();
+    assert_eq!(iter.try_rfold(0_i8, |acc, &x| acc.checked_add(x)), None);
+    assert_eq!(iter.next_back(), Some(&60));
+}
+
+#[test]
+fn test_cloned_try_folds() {
+    let a = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    let f_ref = &|acc, &x| i32::checked_add(2*acc, x);
+    assert_eq!(a.iter().cloned().try_fold(7, f), a.iter().try_fold(7, f_ref));
+    assert_eq!(a.iter().cloned().try_rfold(7, f), a.iter().try_rfold(7, f_ref));
+
+    let a = [10, 20, 30, 40, 100, 60, 70, 80, 90];
+    let mut iter = a.iter().cloned();
+    assert_eq!(iter.try_fold(0_i8, |acc, x| acc.checked_add(x)), None);
+    assert_eq!(iter.next(), Some(60));
+    let mut iter = a.iter().cloned();
+    assert_eq!(iter.try_rfold(0_i8, |acc, x| acc.checked_add(x)), None);
+    assert_eq!(iter.next_back(), Some(70));
+}
+
+#[test]
+fn test_chain_try_folds() {
+    let c = || (0..10).chain(10..20);
+
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!(c().try_fold(7, f), (0..20).try_fold(7, f));
+    assert_eq!(c().try_rfold(7, f), (0..20).rev().try_fold(7, f));
+
+    let mut iter = c();
+    assert_eq!(iter.position(|x| x == 5), Some(5));
+    assert_eq!(iter.next(), Some(6), "stopped in front, state Both");
+    assert_eq!(iter.position(|x| x == 13), Some(6));
+    assert_eq!(iter.next(), Some(14), "stopped in back, state Back");
+    assert_eq!(iter.try_fold(0, |acc, x| Some(acc+x)), Some((15..20).sum()));
+
+    let mut iter = c().rev(); // use rev to access try_rfold
+    assert_eq!(iter.position(|x| x == 15), Some(4));
+    assert_eq!(iter.next(), Some(14), "stopped in back, state Both");
+    assert_eq!(iter.position(|x| x == 5), Some(8));
+    assert_eq!(iter.next(), Some(4), "stopped in front, state Front");
+    assert_eq!(iter.try_fold(0, |acc, x| Some(acc+x)), Some((0..4).sum()));
+
+    let mut iter = c();
+    iter.by_ref().rev().nth(14); // skip the last 15, ending in state Front
+    assert_eq!(iter.try_fold(7, f), (0..5).try_fold(7, f));
+
+    let mut iter = c();
+    iter.nth(14); // skip the first 15, ending in state Back
+    assert_eq!(iter.try_rfold(7, f), (15..20).try_rfold(7, f));
+}
+
+#[test]
+fn test_map_try_folds() {
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!((0..10).map(|x| x+3).try_fold(7, f), (3..13).try_fold(7, f));
+    assert_eq!((0..10).map(|x| x+3).try_rfold(7, f), (3..13).try_rfold(7, f));
+
+    let mut iter = (0..40).map(|x| x+10);
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.next(), Some(20));
+    assert_eq!(iter.try_rfold(0, i8::checked_add), None);
+    assert_eq!(iter.next_back(), Some(46));
+}
+
+#[test]
+fn test_filter_try_folds() {
+    fn p(&x: &i32) -> bool { 0 <= x && x < 10 }
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!((-10..20).filter(p).try_fold(7, f), (0..10).try_fold(7, f));
+    assert_eq!((-10..20).filter(p).try_rfold(7, f), (0..10).try_rfold(7, f));
+
+    let mut iter = (0..40).filter(|&x| x % 2 == 1);
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.next(), Some(25));
+    assert_eq!(iter.try_rfold(0, i8::checked_add), None);
+    assert_eq!(iter.next_back(), Some(31));
+}
+
+#[test]
+fn test_filter_map_try_folds() {
+    let mp = &|x| if 0 <= x && x < 10 { Some(x*2) } else { None };
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!((-9..20).filter_map(mp).try_fold(7, f), (0..10).map(|x| 2*x).try_fold(7, f));
+    assert_eq!((-9..20).filter_map(mp).try_rfold(7, f), (0..10).map(|x| 2*x).try_rfold(7, f));
+
+    let mut iter = (0..40).filter_map(|x| if x%2 == 1 { None } else { Some(x*2 + 10) });
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.next(), Some(38));
+    assert_eq!(iter.try_rfold(0, i8::checked_add), None);
+    assert_eq!(iter.next_back(), Some(78));
+}
+
+#[test]
+fn test_enumerate_try_folds() {
+    let f = &|acc, (i, x)| usize::checked_add(2*acc, x/(i+1) + i);
+    assert_eq!((9..18).enumerate().try_fold(7, f), (0..9).map(|i| (i, i+9)).try_fold(7, f));
+    assert_eq!((9..18).enumerate().try_rfold(7, f), (0..9).map(|i| (i, i+9)).try_rfold(7, f));
+
+    let mut iter = (100..200).enumerate();
+    let f = &|acc, (i, x)| u8::checked_add(acc, u8::checked_div(x, i as u8 + 1)?);
+    assert_eq!(iter.try_fold(0, f), None);
+    assert_eq!(iter.next(), Some((7, 107)));
+    assert_eq!(iter.try_rfold(0, f), None);
+    assert_eq!(iter.next_back(), Some((11, 111)));
+}
+
+#[test]
+fn test_peek_try_fold() {
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!((1..20).peekable().try_fold(7, f), (1..20).try_fold(7, f));
+    let mut iter = (1..20).peekable();
+    assert_eq!(iter.peek(), Some(&1));
+    assert_eq!(iter.try_fold(7, f), (1..20).try_fold(7, f));
+
+    let mut iter = [100, 20, 30, 40, 50, 60, 70].iter().cloned().peekable();
+    assert_eq!(iter.peek(), Some(&100));
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.peek(), Some(&40));
+}
+
+#[test]
+fn test_skip_while_try_fold() {
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    fn p(&x: &i32) -> bool { (x % 10) <= 5 }
+    assert_eq!((1..20).skip_while(p).try_fold(7, f), (6..20).try_fold(7, f));
+    let mut iter = (1..20).skip_while(p);
+    assert_eq!(iter.nth(5), Some(11));
+    assert_eq!(iter.try_fold(7, f), (12..20).try_fold(7, f));
+
+    let mut iter = (0..50).skip_while(|&x| (x % 20) < 15);
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.next(), Some(23));
+}
+
+#[test]
+fn test_take_while_folds() {
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!((1..20).take_while(|&x| x != 10).try_fold(7, f), (1..10).try_fold(7, f));
+    let mut iter = (1..20).take_while(|&x| x != 10);
+    assert_eq!(iter.try_fold(0, |x, y| Some(x+y)), Some((1..10).sum()));
+    assert_eq!(iter.next(), None, "flag should be set");
+    let iter = (1..20).take_while(|&x| x != 10);
+    assert_eq!(iter.fold(0, |x, y| x+y), (1..10).sum());
+
+    let mut iter = (10..50).take_while(|&x| x != 40);
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.next(), Some(20));
+}
+
+#[test]
+fn test_skip_try_folds() {
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!((1..20).skip(9).try_fold(7, f), (10..20).try_fold(7, f));
+    assert_eq!((1..20).skip(9).try_rfold(7, f), (10..20).try_rfold(7, f));
+
+    let mut iter = (0..30).skip(10);
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.next(), Some(20));
+    assert_eq!(iter.try_rfold(0, i8::checked_add), None);
+    assert_eq!(iter.next_back(), Some(24));
+}
+
+#[test]
+fn test_take_try_folds() {
+    let f = &|acc, x| i32::checked_add(2*acc, x);
+    assert_eq!((10..30).take(10).try_fold(7, f), (10..20).try_fold(7, f));
+    //assert_eq!((10..30).take(10).try_rfold(7, f), (10..20).try_rfold(7, f));
+
+    let mut iter = (10..30).take(20);
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.next(), Some(20));
+    //assert_eq!(iter.try_rfold(0, i8::checked_add), None);
+    //assert_eq!(iter.next_back(), Some(24));
+}
+
+#[test]
+fn test_flat_map_try_folds() {
+    let f = &|acc, x| i32::checked_add(acc*2/3, x);
+    let mr = &|x| (5*x)..(5*x + 5);
+    assert_eq!((0..10).flat_map(mr).try_fold(7, f), (0..50).try_fold(7, f));
+    assert_eq!((0..10).flat_map(mr).try_rfold(7, f), (0..50).try_rfold(7, f));
+    let mut iter = (0..10).flat_map(mr);
+    iter.next(); iter.next_back(); // have front and back iters in progress
+    assert_eq!(iter.try_rfold(7, f), (1..49).try_rfold(7, f));
+
+    let mut iter = (0..10).flat_map(|x| (4*x)..(4*x + 4));
+    assert_eq!(iter.try_fold(0, i8::checked_add), None);
+    assert_eq!(iter.next(), Some(17));
+    assert_eq!(iter.try_rfold(0, i8::checked_add), None);
+    assert_eq!(iter.next_back(), Some(35));
+}
diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index 47995597a0a..0e445cdac35 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -24,9 +24,10 @@
 #![feature(i128_type)]
 #![feature(inclusive_range)]
 #![feature(inclusive_range_syntax)]
+#![feature(iterator_try_fold)]
 #![feature(iter_rfind)]
+#![feature(iter_rfold)]
 #![feature(nonzero)]
-#![feature(rand)]
 #![feature(raw)]
 #![feature(refcell_replace_swap)]
 #![feature(sip_hash_13)]
@@ -38,15 +39,11 @@
 #![feature(test)]
 #![feature(trusted_len)]
 #![feature(try_from)]
+#![feature(try_trait)]
 #![feature(unique)]
 
-#![feature(const_atomic_bool_new)]
-#![feature(const_atomic_usize_new)]
-#![feature(const_atomic_isize_new)]
-
 extern crate core;
 extern crate test;
-extern crate rand;
 
 mod any;
 mod array;
diff --git a/src/libcore/tests/mem.rs b/src/libcore/tests/mem.rs
index 86e59c736ba..f55a1c81463 100644
--- a/src/libcore/tests/mem.rs
+++ b/src/libcore/tests/mem.rs
@@ -121,3 +121,19 @@ fn test_transmute() {
     }
 }
 
+#[test]
+#[allow(dead_code)]
+fn test_discriminant_send_sync() {
+    enum Regular {
+        A,
+        B(i32)
+    }
+    enum NotSendSync {
+        A(*const i32)
+    }
+
+    fn is_send_sync<T: Send + Sync>() { }
+
+    is_send_sync::<Discriminant<Regular>>();
+    is_send_sync::<Discriminant<NotSendSync>>();
+}
diff --git a/src/libcore/tests/num/flt2dec/estimator.rs b/src/libcore/tests/num/flt2dec/estimator.rs
index 0bca616ea9a..857aae72c8a 100644
--- a/src/libcore/tests/num/flt2dec/estimator.rs
+++ b/src/libcore/tests/num/flt2dec/estimator.rs
@@ -8,11 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// FIXME https://github.com/kripken/emscripten/issues/4563
-// NB we have to actually not compile this test to avoid
-// an undefined symbol error
-#![cfg(not(target_os = "emscripten"))]
-
 use core::num::flt2dec::estimator::*;
 
 #[test]
diff --git a/src/libcore/tests/num/flt2dec/mod.rs b/src/libcore/tests/num/flt2dec/mod.rs
index 0f4d19e7092..ef0178815f9 100644
--- a/src/libcore/tests/num/flt2dec/mod.rs
+++ b/src/libcore/tests/num/flt2dec/mod.rs
@@ -9,10 +9,7 @@
 // except according to those terms.
 
 use std::prelude::v1::*;
-use std::{str, mem, i16, f32, f64, fmt};
-use std::__rand as rand;
-use rand::{Rand, XorShiftRng};
-use rand::distributions::{IndependentSample, Range};
+use std::{str, i16, f32, f64, fmt};
 
 use core::num::flt2dec::{decode, DecodableFloat, FullDecoded, Decoded};
 use core::num::flt2dec::{MAX_SIG_DIGITS, round_up, Part, Formatted, Sign};
@@ -464,87 +461,6 @@ pub fn more_shortest_sanity_test<F>(mut f: F) where F: FnMut(&Decoded, &mut [u8]
                       exp: 0, inclusive: false} => b"99999999999999999", 17);
 }
 
-fn iterate<F, G, V>(func: &str, k: usize, n: usize, mut f: F, mut g: G, mut v: V) -> (usize, usize)
-        where F: FnMut(&Decoded, &mut [u8]) -> Option<(usize, i16)>,
-              G: FnMut(&Decoded, &mut [u8]) -> (usize, i16),
-              V: FnMut(usize) -> Decoded {
-    assert!(k <= 1024);
-
-    let mut npassed = 0; // f(x) = Some(g(x))
-    let mut nignored = 0; // f(x) = None
-
-    for i in 0..n {
-        if (i & 0xfffff) == 0 {
-            println!("in progress, {:x}/{:x} (ignored={} passed={} failed={})",
-                     i, n, nignored, npassed, i - nignored - npassed);
-        }
-
-        let decoded = v(i);
-        let mut buf1 = [0; 1024];
-        if let Some((len1, e1)) = f(&decoded, &mut buf1[..k]) {
-            let mut buf2 = [0; 1024];
-            let (len2, e2) = g(&decoded, &mut buf2[..k]);
-            if e1 == e2 && &buf1[..len1] == &buf2[..len2] {
-                npassed += 1;
-            } else {
-                println!("equivalence test failed, {:x}/{:x}: {:?} f(i)={}e{} g(i)={}e{}",
-                         i, n, decoded, str::from_utf8(&buf1[..len1]).unwrap(), e1,
-                                        str::from_utf8(&buf2[..len2]).unwrap(), e2);
-            }
-        } else {
-            nignored += 1;
-        }
-    }
-    println!("{}({}): done, ignored={} passed={} failed={}",
-             func, k, nignored, npassed, n - nignored - npassed);
-    assert!(nignored + npassed == n,
-            "{}({}): {} out of {} values returns an incorrect value!",
-            func, k, n - nignored - npassed, n);
-    (npassed, nignored)
-}
-
-pub fn f32_random_equivalence_test<F, G>(f: F, g: G, k: usize, n: usize)
-        where F: FnMut(&Decoded, &mut [u8]) -> Option<(usize, i16)>,
-              G: FnMut(&Decoded, &mut [u8]) -> (usize, i16) {
-    let mut rng: XorShiftRng = Rand::rand(&mut rand::thread_rng());
-    let f32_range = Range::new(0x0000_0001u32, 0x7f80_0000);
-    iterate("f32_random_equivalence_test", k, n, f, g, |_| {
-        let i: u32 = f32_range.ind_sample(&mut rng);
-        let x: f32 = unsafe {mem::transmute(i)};
-        decode_finite(x)
-    });
-}
-
-pub fn f64_random_equivalence_test<F, G>(f: F, g: G, k: usize, n: usize)
-        where F: FnMut(&Decoded, &mut [u8]) -> Option<(usize, i16)>,
-              G: FnMut(&Decoded, &mut [u8]) -> (usize, i16) {
-    let mut rng: XorShiftRng = Rand::rand(&mut rand::thread_rng());
-    let f64_range = Range::new(0x0000_0000_0000_0001u64, 0x7ff0_0000_0000_0000);
-    iterate("f64_random_equivalence_test", k, n, f, g, |_| {
-        let i: u64 = f64_range.ind_sample(&mut rng);
-        let x: f64 = unsafe {mem::transmute(i)};
-        decode_finite(x)
-    });
-}
-
-pub fn f32_exhaustive_equivalence_test<F, G>(f: F, g: G, k: usize)
-        where F: FnMut(&Decoded, &mut [u8]) -> Option<(usize, i16)>,
-              G: FnMut(&Decoded, &mut [u8]) -> (usize, i16) {
-    // we have only 2^23 * (2^8 - 1) - 1 = 2,139,095,039 positive finite f32 values,
-    // so why not simply testing all of them?
-    //
-    // this is of course very stressful (and thus should be behind an `#[ignore]` attribute),
-    // but with `-C opt-level=3 -C lto` this only takes about an hour or so.
-
-    // iterate from 0x0000_0001 to 0x7f7f_ffff, i.e. all finite ranges
-    let (npassed, nignored) = iterate("f32_exhaustive_equivalence_test",
-                                      k, 0x7f7f_ffff, f, g, |i: usize| {
-        let x: f32 = unsafe {mem::transmute(i as u32 + 1)};
-        decode_finite(x)
-    });
-    assert_eq!((npassed, nignored), (2121451881, 17643158));
-}
-
 fn to_string_with_parts<F>(mut f: F) -> String
         where F: for<'a> FnMut(&'a mut [u8], &'a mut [Part<'a>]) -> Formatted<'a> {
     let mut buf = [0; 1024];
diff --git a/src/libcore/tests/num/flt2dec/strategy/grisu.rs b/src/libcore/tests/num/flt2dec/strategy/grisu.rs
index 17fb99bcc92..286b39d8cf3 100644
--- a/src/libcore/tests/num/flt2dec/strategy/grisu.rs
+++ b/src/libcore/tests/num/flt2dec/strategy/grisu.rs
@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::i16;
 use super::super::*;
 use core::num::flt2dec::strategy::grisu::*;
 
@@ -47,35 +46,6 @@ fn shortest_sanity_test() {
 }
 
 #[test]
-fn shortest_random_equivalence_test() {
-    use core::num::flt2dec::strategy::dragon::format_shortest as fallback;
-    f64_random_equivalence_test(format_shortest_opt, fallback, MAX_SIG_DIGITS, 10_000);
-    f32_random_equivalence_test(format_shortest_opt, fallback, MAX_SIG_DIGITS, 10_000);
-}
-
-#[test] #[ignore] // it is too expensive
-fn shortest_f32_exhaustive_equivalence_test() {
-    // it is hard to directly test the optimality of the output, but we can at least test if
-    // two different algorithms agree to each other.
-    //
-    // this reports the progress and the number of f32 values returned `None`.
-    // with `--nocapture` (and plenty of time and appropriate rustc flags), this should print:
-    // `done, ignored=17643158 passed=2121451881 failed=0`.
-
-    use core::num::flt2dec::strategy::dragon::format_shortest as fallback;
-    f32_exhaustive_equivalence_test(format_shortest_opt, fallback, MAX_SIG_DIGITS);
-}
-
-#[test] #[ignore] // it is too expensive
-fn shortest_f64_hard_random_equivalence_test() {
-    // this again probably has to use appropriate rustc flags.
-
-    use core::num::flt2dec::strategy::dragon::format_shortest as fallback;
-    f64_random_equivalence_test(format_shortest_opt, fallback,
-                                         MAX_SIG_DIGITS, 100_000_000);
-}
-
-#[test]
 fn exact_sanity_test() {
     // See comments in dragon.rs's exact_sanity_test for why this test is
     // ignored on MSVC
@@ -86,24 +56,6 @@ fn exact_sanity_test() {
 }
 
 #[test]
-fn exact_f32_random_equivalence_test() {
-    use core::num::flt2dec::strategy::dragon::format_exact as fallback;
-    for k in 1..21 {
-        f32_random_equivalence_test(|d, buf| format_exact_opt(d, buf, i16::MIN),
-                                             |d, buf| fallback(d, buf, i16::MIN), k, 1_000);
-    }
-}
-
-#[test]
-fn exact_f64_random_equivalence_test() {
-    use core::num::flt2dec::strategy::dragon::format_exact as fallback;
-    for k in 1..21 {
-        f64_random_equivalence_test(|d, buf| format_exact_opt(d, buf, i16::MIN),
-                                             |d, buf| fallback(d, buf, i16::MIN), k, 1_000);
-    }
-}
-
-#[test]
 fn test_to_shortest_str() {
     to_shortest_str_test(format_shortest);
 }
diff --git a/src/libcore/tests/num/mod.rs b/src/libcore/tests/num/mod.rs
index 400d53ce51a..7eb5ff98857 100644
--- a/src/libcore/tests/num/mod.rs
+++ b/src/libcore/tests/num/mod.rs
@@ -8,10 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::convert::TryFrom;
+use core::convert::{TryFrom, TryInto};
 use core::cmp::PartialEq;
 use core::fmt::Debug;
 use core::marker::Copy;
+use core::num::TryFromIntError;
 use core::ops::{Add, Sub, Mul, Div, Rem};
 use core::option::Option;
 use core::option::Option::{Some, None};
@@ -134,6 +135,13 @@ fn test_empty() {
     assert_eq!("".parse::<u8>().ok(), None);
 }
 
+#[test]
+fn test_infallible_try_from_int_error() {
+    let func = |x: i8| -> Result<i32, TryFromIntError> { Ok(x.try_into()?) };
+
+    assert!(func(0).is_ok());
+}
+
 macro_rules! test_impl_from {
     ($fn_name: ident, $Small: ty, $Large: ty) => {
         #[test]
diff --git a/src/libcore/tests/option.rs b/src/libcore/tests/option.rs
index 6bac55575fb..22109e28edd 100644
--- a/src/libcore/tests/option.rs
+++ b/src/libcore/tests/option.rs
@@ -270,3 +270,30 @@ fn test_cloned() {
     assert_eq!(opt_ref_ref.clone().cloned(), Some(&val));
     assert_eq!(opt_ref_ref.cloned().cloned(), Some(1));
 }
+
+#[test]
+fn test_try() {
+    fn try_option_some() -> Option<u8> {
+        let val = Some(1)?;
+        Some(val)
+    }
+    assert_eq!(try_option_some(), Some(1));
+
+    fn try_option_none() -> Option<u8> {
+        let val = None?;
+        Some(val)
+    }
+    assert_eq!(try_option_none(), None);
+
+    fn try_option_ok() -> Result<u8, NoneError> {
+        let val = Some(1)?;
+        Ok(val)
+    }
+    assert_eq!(try_option_ok(), Ok(1));
+
+    fn try_option_err() -> Result<u8, NoneError> {
+        let val = None?;
+        Ok(val)
+    }
+    assert_eq!(try_option_err(), Err(NoneError));
+}
diff --git a/src/libcore/tests/ptr.rs b/src/libcore/tests/ptr.rs
index c2d53840f8f..98436f0e1d1 100644
--- a/src/libcore/tests/ptr.rs
+++ b/src/libcore/tests/ptr.rs
@@ -62,6 +62,39 @@ fn test_is_null() {
 
     let mq = unsafe { mp.offset(1) };
     assert!(!mq.is_null());
+
+    // Pointers to unsized types -- slices
+    let s: &mut [u8] = &mut [1, 2, 3];
+    let cs: *const [u8] = s;
+    assert!(!cs.is_null());
+
+    let ms: *mut [u8] = s;
+    assert!(!ms.is_null());
+
+    let cz: *const [u8] = &[];
+    assert!(!cz.is_null());
+
+    let mz: *mut [u8] = &mut [];
+    assert!(!mz.is_null());
+
+    let ncs: *const [u8] = null::<[u8; 3]>();
+    assert!(ncs.is_null());
+
+    let nms: *mut [u8] = null_mut::<[u8; 3]>();
+    assert!(nms.is_null());
+
+    // Pointers to unsized types -- trait objects
+    let ci: *const ToString = &3;
+    assert!(!ci.is_null());
+
+    let mi: *mut ToString = &mut 3;
+    assert!(!mi.is_null());
+
+    let nci: *const ToString = null::<isize>();
+    assert!(nci.is_null());
+
+    let nmi: *mut ToString = null_mut::<isize>();
+    assert!(nmi.is_null());
 }
 
 #[test]
@@ -85,6 +118,39 @@ fn test_as_ref() {
             let p = &u as *const isize;
             assert_eq!(p.as_ref().unwrap(), &2);
         }
+
+        // Pointers to unsized types -- slices
+        let s: &mut [u8] = &mut [1, 2, 3];
+        let cs: *const [u8] = s;
+        assert_eq!(cs.as_ref(), Some(&*s));
+
+        let ms: *mut [u8] = s;
+        assert_eq!(ms.as_ref(), Some(&*s));
+
+        let cz: *const [u8] = &[];
+        assert_eq!(cz.as_ref(), Some(&[][..]));
+
+        let mz: *mut [u8] = &mut [];
+        assert_eq!(mz.as_ref(), Some(&[][..]));
+
+        let ncs: *const [u8] = null::<[u8; 3]>();
+        assert_eq!(ncs.as_ref(), None);
+
+        let nms: *mut [u8] = null_mut::<[u8; 3]>();
+        assert_eq!(nms.as_ref(), None);
+
+        // Pointers to unsized types -- trait objects
+        let ci: *const ToString = &3;
+        assert!(ci.as_ref().is_some());
+
+        let mi: *mut ToString = &mut 3;
+        assert!(mi.as_ref().is_some());
+
+        let nci: *const ToString = null::<isize>();
+        assert!(nci.as_ref().is_none());
+
+        let nmi: *mut ToString = null_mut::<isize>();
+        assert!(nmi.as_ref().is_none());
     }
 }
 
@@ -103,6 +169,24 @@ fn test_as_mut() {
             let p = &mut u as *mut isize;
             assert!(p.as_mut().unwrap() == &mut 2);
         }
+
+        // Pointers to unsized types -- slices
+        let s: &mut [u8] = &mut [1, 2, 3];
+        let ms: *mut [u8] = s;
+        assert_eq!(ms.as_mut(), Some(s));
+
+        let mz: *mut [u8] = &mut [];
+        assert_eq!(mz.as_mut(), Some(&mut [][..]));
+
+        let nms: *mut [u8] = null_mut::<[u8; 3]>();
+        assert_eq!(nms.as_mut(), None);
+
+        // Pointers to unsized types -- trait objects
+        let mi: *mut ToString = &mut 3;
+        assert!(mi.as_mut().is_some());
+
+        let nmi: *mut ToString = null_mut::<isize>();
+        assert!(nmi.as_mut().is_none());
     }
 }
 
diff --git a/src/libcore/tests/result.rs b/src/libcore/tests/result.rs
index 4c5f19dee12..ce41bde8342 100644
--- a/src/libcore/tests/result.rs
+++ b/src/libcore/tests/result.rs
@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use core::option::*;
+
 fn op1() -> Result<isize, &'static str> { Ok(666) }
 fn op2() -> Result<isize, &'static str> { Err("sadface") }
 
@@ -202,3 +204,30 @@ pub fn test_unwrap_or_default() {
     assert_eq!(op1().unwrap_or_default(), 666);
     assert_eq!(op2().unwrap_or_default(), 0);
 }
+
+#[test]
+fn test_try() {
+    fn try_result_some() -> Option<u8> {
+        let val = Ok(1)?;
+        Some(val)
+    }
+    assert_eq!(try_result_some(), Some(1));
+
+    fn try_result_none() -> Option<u8> {
+        let val = Err(NoneError)?;
+        Some(val)
+    }
+    assert_eq!(try_result_none(), None);
+
+    fn try_result_ok() -> Result<u8, u8> {
+        let val = Ok(1)?;
+        Ok(val)
+    }
+    assert_eq!(try_result_ok(), Ok(1));
+
+    fn try_result_err() -> Result<u8, u8> {
+        let val = Err(1)?;
+        Ok(val)
+    }
+    assert_eq!(try_result_err(), Err(1));
+}
diff --git a/src/libcore/tests/slice.rs b/src/libcore/tests/slice.rs
index 8c31d2e83d3..fa4c2e9b373 100644
--- a/src/libcore/tests/slice.rs
+++ b/src/libcore/tests/slice.rs
@@ -8,29 +8,63 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::cmp::Ordering::{Equal, Greater, Less};
-use core::slice::heapsort;
 use core::result::Result::{Ok, Err};
-use rand::{Rng, XorShiftRng};
 
 #[test]
 fn test_binary_search() {
+    let b: [i32; 0] = [];
+    assert_eq!(b.binary_search(&5), Err(0));
+
+    let b = [4];
+    assert_eq!(b.binary_search(&3), Err(0));
+    assert_eq!(b.binary_search(&4), Ok(0));
+    assert_eq!(b.binary_search(&5), Err(1));
+
     let b = [1, 2, 4, 6, 8, 9];
-    assert!(b.binary_search_by(|v| v.cmp(&6)) == Ok(3));
-    assert!(b.binary_search_by(|v| v.cmp(&5)) == Err(3));
-    let b = [1, 2, 4, 6, 7, 8, 9];
-    assert!(b.binary_search_by(|v| v.cmp(&6)) == Ok(3));
-    assert!(b.binary_search_by(|v| v.cmp(&5)) == Err(3));
-    let b = [1, 2, 4, 6, 8, 9];
-    assert!(b.binary_search_by(|v| v.cmp(&8)) == Ok(4));
-    assert!(b.binary_search_by(|v| v.cmp(&7)) == Err(4));
+    assert_eq!(b.binary_search(&5), Err(3));
+    assert_eq!(b.binary_search(&6), Ok(3));
+    assert_eq!(b.binary_search(&7), Err(4));
+    assert_eq!(b.binary_search(&8), Ok(4));
+
+    let b = [1, 2, 4, 5, 6, 8];
+    assert_eq!(b.binary_search(&9), Err(6));
+
     let b = [1, 2, 4, 6, 7, 8, 9];
-    assert!(b.binary_search_by(|v| v.cmp(&8)) == Ok(5));
+    assert_eq!(b.binary_search(&6), Ok(3));
+    assert_eq!(b.binary_search(&5), Err(3));
+    assert_eq!(b.binary_search(&8), Ok(5));
+
     let b = [1, 2, 4, 5, 6, 8, 9];
-    assert!(b.binary_search_by(|v| v.cmp(&7)) == Err(5));
-    assert!(b.binary_search_by(|v| v.cmp(&0)) == Err(0));
-    let b = [1, 2, 4, 5, 6, 8];
-    assert!(b.binary_search_by(|v| v.cmp(&9)) == Err(6));
+    assert_eq!(b.binary_search(&7), Err(5));
+    assert_eq!(b.binary_search(&0), Err(0));
+
+    let b = [1, 3, 3, 3, 7];
+    assert_eq!(b.binary_search(&0), Err(0));
+    assert_eq!(b.binary_search(&1), Ok(0));
+    assert_eq!(b.binary_search(&2), Err(1));
+    assert!(match b.binary_search(&3) { Ok(1...3) => true, _ => false });
+    assert!(match b.binary_search(&3) { Ok(1...3) => true, _ => false });
+    assert_eq!(b.binary_search(&4), Err(4));
+    assert_eq!(b.binary_search(&5), Err(4));
+    assert_eq!(b.binary_search(&6), Err(4));
+    assert_eq!(b.binary_search(&7), Ok(4));
+    assert_eq!(b.binary_search(&8), Err(5));
+}
+
+#[test]
+// Test implementation specific behavior when finding equivalent elements.
+// It is ok to break this test but when you do a crater run is highly advisable.
+fn test_binary_search_implementation_details() {
+    let b = [1, 1, 2, 2, 3, 3, 3];
+    assert_eq!(b.binary_search(&1), Ok(1));
+    assert_eq!(b.binary_search(&2), Ok(3));
+    assert_eq!(b.binary_search(&3), Ok(6));
+    let b = [1, 1, 1, 1, 1, 3, 3, 3, 3];
+    assert_eq!(b.binary_search(&1), Ok(4));
+    assert_eq!(b.binary_search(&3), Ok(8));
+    let b = [1, 1, 1, 1, 3, 3, 3, 3, 3];
+    assert_eq!(b.binary_search(&1), Ok(3));
+    assert_eq!(b.binary_search(&3), Ok(8));
 }
 
 #[test]
@@ -239,6 +273,23 @@ fn test_find_rfind() {
 }
 
 #[test]
+fn test_iter_folds() {
+    let a = [1, 2, 3, 4, 5]; // len>4 so the unroll is used
+    assert_eq!(a.iter().fold(0, |acc, &x| 2*acc + x), 57);
+    assert_eq!(a.iter().rfold(0, |acc, &x| 2*acc + x), 129);
+    let fold = |acc: i32, &x| acc.checked_mul(2)?.checked_add(x);
+    assert_eq!(a.iter().try_fold(0, &fold), Some(57));
+    assert_eq!(a.iter().try_rfold(0, &fold), Some(129));
+
+    // short-circuiting try_fold, through other methods
+    let a = [0, 1, 2, 3, 5, 5, 5, 7, 8, 9];
+    let mut iter = a.iter();
+    assert_eq!(iter.position(|&x| x == 3), Some(3));
+    assert_eq!(iter.rfind(|&&x| x == 5), Some(&5));
+    assert_eq!(iter.len(), 2);
+}
+
+#[test]
 fn test_rotate() {
     const N: usize = 600;
     let a: &mut [_] = &mut [0; N];
@@ -253,68 +304,3 @@ fn test_rotate() {
         assert_eq!(a[(i+k)%N], i);
     }
 }
-
-#[test]
-fn sort_unstable() {
-    let mut v = [0; 600];
-    let mut tmp = [0; 600];
-    let mut rng = XorShiftRng::new_unseeded();
-
-    for len in (2..25).chain(500..510) {
-        let v = &mut v[0..len];
-        let tmp = &mut tmp[0..len];
-
-        for &modulus in &[5, 10, 100, 1000] {
-            for _ in 0..100 {
-                for i in 0..len {
-                    v[i] = rng.gen::<i32>() % modulus;
-                }
-
-                // Sort in default order.
-                tmp.copy_from_slice(v);
-                tmp.sort_unstable();
-                assert!(tmp.windows(2).all(|w| w[0] <= w[1]));
-
-                // Sort in ascending order.
-                tmp.copy_from_slice(v);
-                tmp.sort_unstable_by(|a, b| a.cmp(b));
-                assert!(tmp.windows(2).all(|w| w[0] <= w[1]));
-
-                // Sort in descending order.
-                tmp.copy_from_slice(v);
-                tmp.sort_unstable_by(|a, b| b.cmp(a));
-                assert!(tmp.windows(2).all(|w| w[0] >= w[1]));
-
-                // Test heapsort using `<` operator.
-                tmp.copy_from_slice(v);
-                heapsort(tmp, |a, b| a < b);
-                assert!(tmp.windows(2).all(|w| w[0] <= w[1]));
-
-                // Test heapsort using `>` operator.
-                tmp.copy_from_slice(v);
-                heapsort(tmp, |a, b| a > b);
-                assert!(tmp.windows(2).all(|w| w[0] >= w[1]));
-            }
-        }
-    }
-
-    // Sort using a completely random comparison function.
-    // This will reorder the elements *somehow*, but won't panic.
-    for i in 0..v.len() {
-        v[i] = i as i32;
-    }
-    v.sort_unstable_by(|_, _| *rng.choose(&[Less, Equal, Greater]).unwrap());
-    v.sort_unstable();
-    for i in 0..v.len() {
-        assert_eq!(v[i], i as i32);
-    }
-
-    // Should not panic.
-    [0i32; 0].sort_unstable();
-    [(); 10].sort_unstable();
-    [(); 100].sort_unstable();
-
-    let mut v = [0xDEADBEEFu64];
-    v.sort_unstable();
-    assert!(v == [0xDEADBEEF]);
-}