...A test suite, And security audits, And most importantly benchmarks.
What it does have is a license which it is GPLv3. So if anyone adds all those changes, they have to make the source code available with the same software license.
In this era tho, licenses (I don't agree with this, but this is what it is) are a matter of "tokens", I speak for a fact knowing multiple relatively-big companies just gobbling GPLv3 projects and rewriting them entirely, some do publish them as well.
What it does have is a license which it is GPLv3. So if anyone adds all those changes, they have to make the source code available with the same software license.