I don't understand how this has anything to do with federal hemp law, under federal law marijuana doesn't have any testing requirements either as it's just plain illegal. So what does California have to gain in testing by dumping hemp into the marijuana bucket at a federal level, neither of which improves the testing requirements in California? California could simply require hemp to be tested, but making hemp federally illegal does nothing on that point.
The only answer I can think of is that hemp grown outside of California was competing with california 'legal' weed, the testing angle is non-sensical since this change in law moves hemp from 'kind of required to be tested (but none of the DEA testing implemented, so it's done privately and sometimes not at all), but poorly' to 'illegal' and marijuana still at 'illegal'.
In general this kind of excuse is used by incumbents to pass laws to thwart competition.
You have some regulatory framework which has already been created by captured regulators, so it has a couple of rules that it ought to have (always the ones pointed to in order to justify it) and then others that exist merely to exclude competitors or make sure fixed costs are high enough that only large incumbents can meet them.
The latter set of rules are unreasonable so the market finds a way around them. The incumbents then call this a "loophole" and insist that the competitors be forced into the entire framework rather than just the subset of reasonable rules they'd be able to satisfy without being destroyed. Which destroys them, as intended.
The only answer I can think of is that hemp grown outside of California was competing with california 'legal' weed, the testing angle is non-sensical since this change in law moves hemp from 'kind of required to be tested (but none of the DEA testing implemented, so it's done privately and sometimes not at all), but poorly' to 'illegal' and marijuana still at 'illegal'.