Add missing test case

src/allocator.rs

@@ -1105,7 +1105,11 @@ impl<E: Env> Allocator<E> {
         }
 
         let new_pointer = self.alloc(align, new_size)?;
-        core::ptr::copy_nonoverlapping(pointer.as_ptr(), new_pointer.as_ptr(), current_size.bytes() as usize);
+        core::ptr::copy_nonoverlapping(
+            pointer.as_ptr(),
+            new_pointer.as_ptr(),
+            core::cmp::min(current_size, new_size).bytes() as usize,
+        );
         self.free(pointer);
 
         Some(new_pointer)

src/lib.rs

@@ -230,6 +230,45 @@ fn test_shrink() {
     unsafe { alloc.free(b) };
 }
 
+#[test]
+fn test_realloc() {
+    let one = Size::from_bytes_usize(1).unwrap();
+    let big = Size::from_bytes_usize(128).unwrap();
+    let small = Size::from_bytes_usize(32).unwrap();
+
+    let mut buffer = Array([0_u8; 512]);
+    let mut alloc = Allocator::new(unsafe { ArrayPointer::new(&mut buffer) });
+
+    let a = alloc.alloc(one, big).unwrap();
+    unsafe {
+        for i in 0..128 {
+            *a.as_ptr().add(i) = i as u8;
+        }
+    }
+
+    let a = unsafe { alloc.realloc(a, one, small) }.unwrap();
+    unsafe {
+        for i in 0..32 {
+            assert_eq!(*a.as_ptr().add(i), i as u8);
+        }
+        alloc.free(a);
+    }
+
+    let b = alloc.alloc(one, small).unwrap();
+    unsafe {
+        for i in 0..32 {
+            *b.as_ptr().add(i) = i as u8;
+        }
+    }
+    let b = unsafe { alloc.realloc(b, one, big) }.unwrap();
+    unsafe {
+        for i in 0..32 {
+            assert_eq!(*b.as_ptr().add(i), i as u8);
+        }
+        alloc.free(b);
+    }
+}
+
 #[test]
 fn test_grow() {
     let one = Size::from_bytes_usize(32).unwrap();