Test Subject 234

Test Subject 234 is an Easter Egg in a form of a Test Subject featured on a clipboard found in the Enrichment Center. 234 apparently passed the tests they took.

It was previously speculated that Chell might be Test Subject 234, since "234" is featured on the bed in her Relaxation Vault, but this was disproved in Portal 2: Lab Rat, which states that Chell was Test Subject #1498, until Doug Rattmann changed her to Test Subject #1.