Add hub tests and example

example/doc_hub_basic.cpp

@@ -0,0 +1,31 @@
+/* Basic example of use of boost::container::hub.
+ * 
+ * Copyright 2026 Joaquin M Lopez Munoz.
+ * Distributed under the Boost Software License, Version 1.0.
+ * (See accompanying file LICENSE_1_0.txt or copy at
+ * http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+#include <boost/container/hub.hpp>
+#ifdef NDEBUG
+#	undef NDEBUG
+#endif
+#include <cassert>
+
+int main()
+{
+  boost::container::hub<int> h;
+
+  // Insert some elements and keep an iterator to one of them
+  for(int i = 0; i < 100; ++i) h.insert(i);
+  auto it = h.insert(100);
+  for(int i = 101; i < 200; ++i) h.insert(i);
+
+  // Erase some of the elements
+  erase_if(h, [](int x) { return x % 2 != 0;});
+  assert(*it == 100); // iterator still valid
+
+  // Insert many more elements
+  for(int i = 200; i < 10000; ++i) h.insert(i);
+  assert(*it == 100); // iterator still valid
+}