function node(value, left, right) {
  var n = {};
  n.value = value;
  n.left = left;
  n.right = right;
  return n;
}


function test_solution(sol) {
  if (!sol.serialize || !sol.deserialize) {
    throw {
      name: 'Solution not in right format',
      message: 'Provide an object with serialize and deserialize functions'
    };
  }
  var randint = function(max) {
    return Math.floor(max * Math.random());
  };

  // create a random tree with the given size
  var random_tree = function(size) {
    var root = {value: randint(1000), left: null, right: null};
    for (var i = 0; i < size; i++) {
      var insert_position = root;
      while (true) {
        if (randint(2) == 0) {
          // add to left
          if (insert_position.left == null) {
            insert_position.left = node(100 + randint(1000), null, null);
            break;
          } else {
            insert_position = insert_position.left;
          }
        } else {
          // add to right
          if (insert_position.right == null) {
            insert_position.right = node(100 + randint(1000), null, null);
            break;
          } else {
            insert_position = insert_position.right;
          }
        }
      }
    }
    return root;
  };

  var trees_equal = function(a, b) {
    if (a == null || b == null) {
      return a == b;
    } else {
      return a.value == b.value &&
        trees_equal(a.left, b.left) &&
        trees_equal(a.right, b.right);
    }
  };

  for (var i = 0; i < 100; i++) {
    var TREE_SIZE = 1 + randint(100);
    var tree = random_tree(TREE_SIZE);
    var serialized = sol.serialize(tree);
    if (serialized.length > TREE_SIZE * 4) {
      throw {
        name: "Serialized tree too large",
        message: "Your serialize function should be more compact!",
      };
    }
    var restored = sol.deserialize(serialized);
    if (!trees_equal(restored, tree)) {
      throw {
        name: "Trees not equal",
        message: "deserialize(serialize(tree)) != tree",
        serialized: serialized,
        original: tree,
        restored: restored
      };
    }
  }
  console.log("Tests passed!");
}