function remove(array, item) {
        var index = array.indexOf(item);
        if (index > -1) {
            array.splice(index, 1);
        }
    }
Add a callback that's triggered when all tests are complete.

@param {Function} callback - Callback function, called with an
array of :js:class:`Test` objects, a :js:class:`TestsStatus`
object and an array of :js:class:`AssertRecord` objects. If the
debug setting is ``false`` the final argument will be an empty
array.

For performance reasons asserts are only tracked when the debug
setting is ``true``. In other cases the array of asserts will be
empty.