[gtkmm] tests: tree_model_iterator: Add simple test of constness issues.

[Murray Cumming <murrayc src gnome org>]

commit a3d0b496d547d229f52828eede871729129eb31d
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Mar 15 09:12:39 2017 +0100

    tests: tree_model_iterator: Add simple test of constness issues.
    
    Bug #134520

 tests/Makefile.am                 |    2 +
 tests/tree_model_iterator/main.cc |   43 +++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 0 deletions(-)
---
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 53301ea..b6211f9 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -31,6 +31,7 @@ check_PROGRAMS =                      \
        property_notification/test      \
        refcount_dialog/test            \
        scrolledwindow/test             \
+       tree_model_iterator/test \
        wrap_existing/test
 
 TESTS =        object_move/test \
@@ -51,6 +52,7 @@ object_move_test_SOURCES           = object_move/main.cc
 property_notification_test_SOURCES = property_notification/main.cc
 refcount_dialog_test_SOURCES       = refcount_dialog/main.cc
 scrolledwindow_test_SOURCES        = scrolledwindow/main.cc
+tree_model_iterator_test_SOURCES   = tree_model_iterator/main.cc
 wrap_existing_test_SOURCES         = wrap_existing/main.cc
 
 gdkmm_includes = -I$(top_builddir)/gdk $(if $(srcdir:.=),-I$(top_srcdir)/gdk)
diff --git a/tests/tree_model_iterator/main.cc b/tests/tree_model_iterator/main.cc
new file mode 100644
index 0000000..dd63173
--- /dev/null
+++ b/tests/tree_model_iterator/main.cc
@@ -0,0 +1,43 @@
+#include <gtkmm.h>
+#include <iostream>
+#include <cassert>
+#include <cstdlib>
+
+static void
+test_const_conversion() {
+  Gtk::TreeModel::iterator non_const_iter;
+  Gtk::TreeModel::const_iterator const_iter;
+  assert(non_const_iter == const_iter);
+  assert(const_iter == non_const_iter);
+}
+
+static void
+test_assignment_from_const() {
+  Gtk::TreeModel::iterator non_const_iter;
+  Gtk::TreeModel::const_iterator const_iter = non_const_iter;
+  assert(const_iter == non_const_iter);
+}
+
+// TODO: Find some way to check that the opposite is not possible.
+// For instance, check that the code won't compile if we try to assign
+// a const iterator to a non-const iterator.
+/*
+static void
+test_assignment_to_const() {
+  Gtk::TreeModel::const_iterator const_iter;
+  // This should not compile:
+  Gtk::TreeModel::iterator non_const_iter = const_iter;
+  assert(const_iter == non_const_iter);
+}
+*/
+
+int main(int /* argc */, char** /* argv */)
+{
+  gtk_init();
+  Gtk::Main::init_gtkmm_internals();
+
+  test_const_conversion();
+  test_assignment_from_const();
+
+  return EXIT_SUCCESS;
+}