See nodeunit -h for the available options (This is for version 0.8.1):
Usage: nodeunit [options] testmodule1.js testfolder [...]
Options:
--config FILE the path to a JSON file with options
--reporter FILE optional path to a reporter file to customize the output
--list-reporters list available build-in reporters
-t name, specify a test to run
-f fullname, specify a specific test to run. fullname is built so: "outerGroup - .. - innerGroup - testName"
-h, --help display this help and exit
-v, --version output version information and exit
So from that the following should do what you want:
$ nodeunit tests.js -t test2
e.g:
$ nodeunit ./tests.js -t test2
tests.js
test2
✔ test2