Script exiting on failed nosetests

Add set -e after the shebang line to make the script exit if any of the command fails:

#!/bin/bash
set -e
git checkout $1
nosetests

From help set:

-e Exit immediately if a command exits with a non-zero status.

You could try the following.

#!/bin/bash
git checkout $1
nosetests || exit 1
git checkout master
git merge $1
git push
git checkout $1

The || will check the return code of nosetests and will execute the command exit 1 if it is non-zero.

Another variant could be.

#!/bin/bash
git checkout $1
if ! nosetests
then
    exit 1
fi
git checkout master
git merge $1
git push
git checkout $1