I have met several school teachers in my time. I have looked at the exam required to become a school teacher. The requirements are very minimal.
Most of the home school parents I meet are intelligent. They have right priorities.
There should be no requirements to home school your own children.
There should be a test, however, at certain junctures, like the end of the first three years, and then every three years thereafter.
The state is not going to institute those exams for two primary reasons:
1. School is really a system of "socialization", that is, thought control.
2. The home schoolers would vastly outperform the public school.