Move cons_end test

examples/tests/lists.nbt

@@ -2,7 +2,6 @@ let xs = [1, 2, 3]
 
 assert_eq(len([]), 0)
 assert_eq(len(xs), 3)
-assert_eq(len(cons_end(xs, 4)), 4)
 
 assert_eq(head(xs), 1)
 assert_eq(head(tail(xs)), 2)
@@ -11,6 +10,9 @@ assert_eq(tail(xs), [2, 3])
 
 assert_eq(cons(0, xs), [0, 1, 2, 3])
 
+assert_eq(cons_end(xs, 4), [1, 2, 3, 4])
+assert_eq(cons_end([], 0), [0])
+
 assert(is_empty([]))
 assert(!is_empty(xs))