Startups require potential engineer hires to perform a test?

One of my first jobs out of school was for a startup, and they required me to do a short hack to prove myself. Then I worked for two larger companies and they didn't require any pretest. Now I'm considering working at another startup, and they want me to perform a test. Do just startups do this? What's your experience... I almost get the feeling that it's free labor for them.