This is approaching things the wrong way. The reason is, the difference between the pressure level of an ultra high vacuum and a more moderate 10-6 torr is very little in terms of pressure. So it is completely sufficient to test for operation at 10^-6 torr rather than 10^-12 if you are looking for general effects of pressure on operation. The only thing that comes to mind that could be a problem is the bonding of metal surfaces to metal surfaces - vacuum welding - and that can be easily tested at 10-6 torr. But as far as leakages go, the absolute worst case would be how much air would leak from a ship at 14 pounds per square inch internal pressure, and there is really no need to test that to 10^-12 torr. The pressure comes from inside, and it is limited to 14 psi whereas the suck pressure can never exceed that level, in other words you would never see a sucking pressure of, say, 1000 psi and hence not need to have a test chamber that can pull that amount.

Added: I confess to an error. There would be tanks of liquid fuels and those might have higher pressures. But again, it is the pressure in the tank and not the vacuum that sets the pressure force level. So you would design the tank walls to handle P=Plf- Pvac where Pvac = 0 worst case.

This is approaching things the wrong way. The reason is, the difference between the pressure level of an ultra high vacuum and a more moderate 10-6 torr is very little in terms of pressure. So it is completely sufficient to test for operation at 10-6 torr rather than 10-12 if you are looking for general effects of pressure on operation. The only thing that comes to mind that could be a problem is the bonding of metal surfaces to metal surfaces - vacuum welding - and that can be easily tested at 10-6 torr. But as far as leakages go, the absolute worst case would be how much air would leak from a ship at 14 pounds per square inch internal pressure, and there is really no need to test that to 10-12 torr. The pressure comes from inside, and it is limited to 14 psi whereas the suck pressure can never exceed that level, in other words you would never see a sucking pressure of, say, 1000 psi and hence not need to have a test chamber that can pull that amount.

Added: I confess to an error. There would be tanks of liquid fuels and those might have higher pressures. But again, it is the pressure in the tank and not the vacuum that sets the pressure force level. So you would design the tank walls to handle P=Plf- Pvac where Pvac = 0 worst case.

This is approaching things the wrong way. The reason is, the difference between the pressure level of an ultra high vacuum and a more moderate 10-6 torr is very little in terms of pressure. So it is completely sufficient to test for operation at 10-6 torr rather than 10-12 if you are looking for general effects of pressure on operation. The only thing that comes to mind that could be a problem is the bonding of metal surfaces to metal surfaces - vacuum welding - and that can be easily tested at 10-6 torr. But as far as leakages go, the absolute worst case would be how much air would leak from a ship at 14 pounds per square inch internal pressure, and there is really no need to test that to 10-12 torr. The pressure comes from inside, and it is limited to 14 psi whereas the suck pressure can never exceed that level, in other words you would never see a sucking pressure of, say, 1000 psi and hence not need to have a test chamber that can pull that amount.