Improve test suite by performing no op swap operation randomly

tests/test-mtree.c

@@ -261,6 +261,7 @@ static void insert(unsigned cmd, unsigned ref)
   assert( cmd < 5);
   assert( ref <= g_num);
   int val = (int) g_num + 1;
+  //printf("Command %d for value %d at %d\n", cmd, val, ref);
   switch (cmd) {
     case 0:
       g_tree[++g_num] = tree_insert_up( g_tree[ref], val);
@@ -299,9 +300,10 @@ static inline unsigned int rand_get(void)
 
 static void test_gen(void)
 {
-  tree_t t;
+  tree_t t, t0;
   string_t s;
   tree_init(t);
+  tree_init(t0);
   string_init(s);
   g_root = g_tree[++ g_num] = tree_set_root(t, 1);
   tree_get_str(s, t, false);
@@ -310,8 +312,15 @@ static void test_gen(void)
     unsigned ref = 1 + (rand_get() % g_num);
     insert(cmd, ref);
     tree_get_str(s, t, false);
+    tree_set(t0, t);
+    unsigned ref1 = 1 + (rand_get() % g_num);
+    unsigned ref2 = 1 + (rand_get() % g_num);
+    tree_swap_at(g_tree[ref1], g_tree[ref2], false);
+    tree_swap_at(g_tree[ref1], g_tree[ref2], false);
+    assert(tree_equal_p(t, t0));
   }
   string_clear(s);
+  tree_clear(t0);
   tree_clear(t);
 }