Move libXtest into libX/tests

This change moves:

1. `libcoretest` into `libcore/tests`
2. `libcollectionstest` into `libcollections/tests`

This is a follow-up to #39561.

src/libcore/tests/mem.rs

@@ -0,0 +1,123 @@
+// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use core::mem::*;
+
+#[test]
+fn size_of_basic() {
+    assert_eq!(size_of::<u8>(), 1);
+    assert_eq!(size_of::<u16>(), 2);
+    assert_eq!(size_of::<u32>(), 4);
+    assert_eq!(size_of::<u64>(), 8);
+}
+
+#[test]
+#[cfg(target_pointer_width = "16")]
+fn size_of_16() {
+    assert_eq!(size_of::<usize>(), 2);
+    assert_eq!(size_of::<*const usize>(), 2);
+}
+
+#[test]
+#[cfg(target_pointer_width = "32")]
+fn size_of_32() {
+    assert_eq!(size_of::<usize>(), 4);
+    assert_eq!(size_of::<*const usize>(), 4);
+}
+
+#[test]
+#[cfg(target_pointer_width = "64")]
+fn size_of_64() {
+    assert_eq!(size_of::<usize>(), 8);
+    assert_eq!(size_of::<*const usize>(), 8);
+}
+
+#[test]
+fn size_of_val_basic() {
+    assert_eq!(size_of_val(&1u8), 1);
+    assert_eq!(size_of_val(&1u16), 2);
+    assert_eq!(size_of_val(&1u32), 4);
+    assert_eq!(size_of_val(&1u64), 8);
+}
+
+#[test]
+fn align_of_basic() {
+    assert_eq!(align_of::<u8>(), 1);
+    assert_eq!(align_of::<u16>(), 2);
+    assert_eq!(align_of::<u32>(), 4);
+}
+
+#[test]
+#[cfg(target_pointer_width = "16")]
+fn align_of_16() {
+    assert_eq!(align_of::<usize>(), 2);
+    assert_eq!(align_of::<*const usize>(), 2);
+}
+
+#[test]
+#[cfg(target_pointer_width = "32")]
+fn align_of_32() {
+    assert_eq!(align_of::<usize>(), 4);
+    assert_eq!(align_of::<*const usize>(), 4);
+}
+
+#[test]
+#[cfg(target_pointer_width = "64")]
+fn align_of_64() {
+    assert_eq!(align_of::<usize>(), 8);
+    assert_eq!(align_of::<*const usize>(), 8);
+}
+
+#[test]
+fn align_of_val_basic() {
+    assert_eq!(align_of_val(&1u8), 1);
+    assert_eq!(align_of_val(&1u16), 2);
+    assert_eq!(align_of_val(&1u32), 4);
+}
+
+#[test]
+fn test_swap() {
+    let mut x = 31337;
+    let mut y = 42;
+    swap(&mut x, &mut y);
+    assert_eq!(x, 42);
+    assert_eq!(y, 31337);
+}
+
+#[test]
+fn test_replace() {
+    let mut x = Some("test".to_string());
+    let y = replace(&mut x, None);
+    assert!(x.is_none());
+    assert!(y.is_some());
+}
+
+#[test]
+fn test_transmute_copy() {
+    assert_eq!(1, unsafe { transmute_copy(&1) });
+}
+
+#[test]
+fn test_transmute() {
+    trait Foo { fn dummy(&self) { } }
+    impl Foo for isize {}
+
+    let a = box 100isize as Box<Foo>;
+    unsafe {
+        let x: ::core::raw::TraitObject = transmute(a);
+        assert!(*(x.data as *const isize) == 100);
+        let _x: Box<Foo> = transmute(x);
+    }
+
+    unsafe {
+        assert_eq!(transmute::<_, Vec<u8>>("L".to_string()), [76]);
+    }
+}
+