add memory arena test (#2298)

* add memory arena test

* add assert

* Update stacker/src/memory_arena.rs

Co-authored-by: Paul Masurel <[email protected]>

---------

Co-authored-by: Paul Masurel <[email protected]>

stacker/src/memory_arena.rs

@@ -189,6 +189,11 @@ struct Page {
 
 impl Page {
     fn new(page_id: usize) -> Page {
+        // We use 32-bits addresses.
+        // - 20 bits for the in-page addressing
+        // - 12 bits for the page id.
+        // This limits us to 2^12 - 1=4095 for the page id.
+        assert!(page_id < 4096);
         Page {
             page_id,
             len: 0,
@@ -238,6 +243,7 @@ impl Page {
 mod tests {
 
     use super::MemoryArena;
+    use crate::memory_arena::PAGE_SIZE;
 
     #[test]
     fn test_arena_allocate_slice() {
@@ -255,6 +261,31 @@ mod tests {
         assert_eq!(arena.slice(addr_b, b.len()), b);
     }
 
+    #[test]
+    fn test_arena_allocate_end_of_page() {
+        let mut arena = MemoryArena::default();
+
+        // A big block
+        let len_a = PAGE_SIZE - 2;
+        let addr_a = arena.allocate_space(len_a);
+        *arena.slice_mut(addr_a, len_a).last_mut().unwrap() = 1;
+
+        // Single bytes
+        let addr_b = arena.allocate_space(1);
+        arena.slice_mut(addr_b, 1)[0] = 2;
+
+        let addr_c = arena.allocate_space(1);
+        arena.slice_mut(addr_c, 1)[0] = 3;
+
+        let addr_d = arena.allocate_space(1);
+        arena.slice_mut(addr_d, 1)[0] = 4;
+
+        assert_eq!(arena.slice(addr_a, len_a)[len_a - 1], 1);
+        assert_eq!(arena.slice(addr_b, 1)[0], 2);
+        assert_eq!(arena.slice(addr_c, 1)[0], 3);
+        assert_eq!(arena.slice(addr_d, 1)[0], 4);
+    }
+
     #[derive(Clone, Copy, Debug, Eq, PartialEq)]
     struct MyTest {
         pub a: usize,