All the various Polkadot runtimes lack basic testing that would help ensure that downstream changes in Substrate would not significantly alter the logic of Polkadot.

Some ideas:

• Verify Weight Assumptions are the Same
• Verify Fees are calculated the same
• Verify constants set in upstream pallets are the same
• Verify transaction priority or whatever else is the same

etc...

We could start by copying/porting Substrate node-runtime tests to Polkadot.