I've created a script for this, it applies the staged changes to a fresh clone and executes the command you specify. To quote from --help:
If you have lots of unrelated uncommitted changes in the current repository and want to split up the commit, how can you easily check if the changes passes the test suite? With all the other unrelated changes it can be hard to make sure that only relevant changes becomes part of the commit, and that they don't result in regressions. This script clones the repository to the directory ".testadd.tmp" in the current directory and applies the staged changes there (unless -u/--unmodified or -p/--pristine is specified), chdirs to the same relative directory in the clone and executes the command specified on the command line there.
If you have lots of unrelated uncommitted changes in the current repository and want to split up the commit, how can you easily check if the changes passes the test suite? With all the other unrelated changes it can be hard to make sure that only relevant changes becomes part of the commit, and that they don't result in regressions. This script clones the repository to the directory ".testadd.tmp" in the current directory and applies the staged changes there (unless -u/--unmodified or -p/--pristine is specified), chdirs to the same relative directory in the clone and executes the command specified on the command line there.
It's available from
https://github.com/sunny256/utils/blob/master/git-testadd
and the test suite (place it in a subdirectory below the script) is at
https://github.com/sunny256/utils/blob/master/tests/git-test...
It's stable, and I've been using it almost every day for 1.5 years. It also works with binary files.