Otherwise, run-test.sh fails with the error:
(file-error "Opening output file" "no such file or directory"
"/tmp/el-get-test-home/.emacs.d/el-get/.status.el.old")
This is useful if you are testing the installation of a package with
lots of dependencies, since without cleaning the dependencies will not
need to be reinstalled at the beginning of each test run.
Now you can say "test/run-test.sh 303" to run the test
"test/el-get-issue-303.el"
Also, give an explicit error message when a test file does not exist.