You can have some required tests but those tests will be a part of the approval process, not all that pass the test get the approval but anyone that fails the test goes hope in shame.
The test could have basic things like a car stopped in the middle of the road, a fake person that is fallen on the ground, a tree on the road, a big stone on the road, a big hole in the road and other similar tests.
You can change the obstacle types and sizes so tests differ.
The company will not be allowed to use a different software fort this tests so at least you can test that the sensors are good enough and that the software can handle basic things.
This tests would be like the medical tests a driver must pass before starting the driving school, we can trust Uber like companies to perform this tests inside before putting the cars on the road for public road testing.
If the tests are too basic I am sure clever people can find even better tests to stress the sensors and software before allowing the dangerous tests on public roads.