Few weeks a go, I was doing some source code merging works. Some features developed in some branches of the repository were merged into some other branches. For the simple merging tasks, we directly use the "svn merge" command. But, in most of the times, we can't achieve what we need just using the "svn merge". That is, because the branches we do the merging between, have been grown largely, and independently.
For these situations, we have to use a good merging tool such as "Meld". Actually, this is the best tool I have ever seen for this task.
"Meld is a visual diff and merge tool. You can compare two or three files and edit them in place (diffs update dynamically). You can compare two or three folders and launch file comparisons. You can browse and view a working copy from popular version control systems such such as CVS, Subversion, Bazaar-ng and Mercurial." [http://meld.sourceforge.net/]
When you merge some thing did by other person in some other branch, there may be some difficulties, because you may don't know the exact files and places to add the modifications. In this type of situations, it is easy to start the merging from known place such as an UI. After merging that known place, you can run the application, and through the error messages you get, you can find all the other places that are to be merged. Usually, you can do this by starting in a place such as an UI and it will end up in a place such as a data base table eventually. Although this method is very simple, I found it is very effective, and you can finish the whole process in a less time. This is a test driven way, so I would like to call it as “Test Driven Merging”.