[gitg] Add checkout_branch convenience test function

[Jesse van den Kieboom <jessevdk src gnome org>]

commit 009e21bd7ae00eba4ddeebd5ca13455e4ec4d3ec
Author: Jesse van den Kieboom <jessevdk gnome org>
Date:   Thu Aug 13 20:04:12 2015 +0200

    Add checkout_branch convenience test function

 tests/support/repository.vala |   21 +++++++++++++++++++++
 1 files changed, 21 insertions(+), 0 deletions(-)
---
diff --git a/tests/support/repository.vala b/tests/support/repository.vala
index a7368aa..0ff97dd 100644
--- a/tests/support/repository.vala
+++ b/tests/support/repository.vala
@@ -324,6 +324,27 @@ class Gitg.Test.Repository : Gitg.Test.Test
                }
        }
 
+       protected void checkout_branch(string name)
+       {
+               try
+               {
+                       var branch = d_repository.lookup_reference_dwim(name) as Gitg.Branch;
+                       var commit = branch.resolve().lookup() as Ggit.Commit;
+                       var tree = commit.get_tree();
+
+                       var opts = new Ggit.CheckoutOptions();
+                       opts.set_strategy(Ggit.CheckoutStrategy.SAFE);
+
+                       d_repository.checkout_tree(tree, opts);
+                       d_repository.set_head(branch.get_name());
+               }
+               catch (Error e)
+               {
+                       assert_no_error(e);
+                       return;
+               }
+       }
+
        protected override void set_up()
        {
                string wd;