If you're suggesting a law against hiring people who have not passed such an exam, the First Amendment would likely be an obstacle (just as the government canno

If you're suggesting a law against hiring people who have not passed such an exam, the First Amendment would likely be an obstacle (just as the government cannot impose an licensure requirement on journalists), since source code is protected speech. However, in safety-critical systems (such as self-driving cars), the government probably can impose a regulation against using code developed by an unlicensed programmer in production. If you're suggesting a de facto industry-standard exam, I think there just isn't enough wide agreement about what should be on the exam.