I create a branch, "test1," change a file, and do not merge it back in master. I forget about the test for a week. I made lots of changes in master since that test1 branch.
But, then I decide I still like that one feature in test1 that I did, a single file I changed.
When I merge the branch test1 into master, what gets merged? Just the test1 file? I don't want to overwrite all my new master files with the old test1 branch files (except that one file I changed).