add other failing test and fix them

core/runtime/default_allocators_arena.odin

@@ -102,14 +102,14 @@ arena_alloc :: proc(arena: ^Arena, size, alignment: uint, loc := #caller_locatio
 	if size == 0 {
 		return
 	}
-
-	if arena.curr_block == nil || (safe_add(arena.curr_block.used, size) or_else 0) > arena.curr_block.capacity {
-		size = align_forward_uint(size, alignment)
+	
+	needed := align_forward_uint(size, alignment)
+	if arena.curr_block == nil || (safe_add(arena.curr_block.used, needed) or_else 0) > arena.curr_block.capacity {
 		if arena.minimum_block_size == 0 {
 			arena.minimum_block_size = DEFAULT_ARENA_GROWING_MINIMUM_BLOCK_SIZE
 		}
 
-		block_size := max(size, arena.minimum_block_size)
+		block_size := max(needed, arena.minimum_block_size)
 
 		if arena.backing_allocator.procedure == nil {
 			arena.backing_allocator = default_allocator()

tests/core/runtime/test_core_runtime.odin

@@ -30,6 +30,7 @@ main :: proc() {
 
 	test_temp_allocator_big_alloc_and_alignment(&t)
 	test_temp_allocator_alignment_boundary(&t)
+	test_temp_allocator_returns_correct_size(&t)
 
 	fmt.printf("%v/%v tests successful.\n", TEST_count - TEST_fail, TEST_count)
 	if TEST_fail > 0 {
@@ -56,6 +57,16 @@ test_temp_allocator_big_alloc_and_alignment :: proc(t: ^testing.T) {
 	context.allocator = runtime.arena_allocator(&arena)
 
 	mappy: map[[8]int]int
-    err := reserve(&mappy, 50000)
+	err := reserve(&mappy, 50000)
 	expect_value(t, err, nil)
 }
+
+@(test)
+test_temp_allocator_returns_correct_size :: proc(t: ^testing.T) {
+	arena: runtime.Arena
+	context.allocator = runtime.arena_allocator(&arena)
+
+	bytes, err := mem.alloc_bytes(10, 16)
+	expect_value(t, err, nil)
+	expect_value(t, len(bytes), 10)
+}