Testing Overflow - GNU libavl 2.0.3

4.14.3 Testing Overflow

Testing for overflow requires an entirely different set of test functions. The idea is to create a too-tall tree using one of the pathological insertion orders (ascending, descending, zig-zag, shifted ascending), then try out each of the functions that can overflow on it and make sure that they behave as they should.

There is a separate test function for each function that can overflow a stack but which is not tested by test(). These functions are called by driver function test_overflow(), which also takes care of creating, populating, and destroying the tree.

123. <BST overflow test function 123> =
<Overflow testers 125>

/* Tests the tree routines for proper handling of overflows.
   Inserting the n elements of order[] should produce a tree
   with height greater than BST_MAX_HEIGHT.
   Uses allocator as the allocator for tree and node data.
   Use verbosity to set the level of chatter on stdout. */
int 
test_overflow (struct libavl_allocator *allocator, 
               int order[], int n, int verbosity) 
{
  /* An overflow tester function. */
  typedef int test_func (struct bst_table *, int n);

  /* An overflow tester. */
  struct test 
    {
      test_func *func;                  /* Tester function. */
      const char *name;                 /* Test name. */
    };

  /* All the overflow testers. */
  static const struct test test[] = 
    {
      {test_bst_t_first, "first item"},
      {test_bst_t_last, "last item"},
      {test_bst_t_find, "find item"},
      {test_bst_t_insert, "insert item"},
      {test_bst_t_next, "next item"},
      {test_bst_t_prev, "previous item"},
      {test_bst_copy, "copy tree"},
    };

  const struct test *i;                 /* Iterator. */

  /* Run all the overflow testers. */
  for (i = test; i < test + sizeof test / sizeof *test; i++) 
    {
      struct bst_table *tree;
      int j;

      if (verbosity >= 2) 
        printf ("  Running %s test...\n", i->name);

      tree = bst_create (compare_ints, NULL, allocator);
      if (tree == NULL) 
        {
          printf ("    Out of memory creating tree.\n");
          return 1;
        }

      for (j = 0; j < n; j++) 
        {
          void **p = bst_probe (tree, &order[j]);
          if (p == NULL || *p != &order[j]) 
            {
              if (p == NULL && verbosity >= 0)
                printf ("    Out of memory in insertion.\n");
              else if (p != NULL) 
                printf ("    Duplicate item in tree!\n");              
              bst_destroy (tree, NULL);
              return p == NULL;
            }
        }

      if (i->func (tree, n) == 0)
        return 0;

      if (verify_tree (tree, order, n) == 0)
        return 0;
      bst_destroy (tree, NULL);
    }

  return 1;
}

This code is included in 99, 188, 240, 292, 332, 370, 413, 451, 484, 517, 550, and 585.

124. <Test prototypes 102> +=
int test_overflow (struct libavl_allocator *, int order[], int n, 
                   int verbosity);

There is an overflow tester for almost every function that can overflow. Here is one example:

125. <Overflow testers 125> =
static int 
test_bst_t_first (struct bst_table *tree, int n) 
{
  struct bst_traverser trav;
  int *first;

  first = bst_t_first (&trav, tree);
  if (first == NULL || *first != 0) 
    {
      printf ("    First item test failed: expected 0, got %d\n",
              first != NULL ? *first : -1);
      return 0;
    }

  return 1;
}