How do you perform a state query in a unit test?

Question

In a custom Substrate pallet unit test, I need to get a list of governance proposals using the chain state. I have used Polkadot JS to query state before but not from within a Substrate unit test in Rust.

Do I need to use a mock? I think I have to create to create the encoded key from the module and method names. This is probably way off but here's what I've come up with:

let key = twox_128("Collective") + twox_128("CouncilProposals");
let encoded_key = scale_encode(key);

let storage_key = blake2_128_concat(encoded_key);
let proposals = state_getStorage(storage_key);

What's the correct way to do it? I need an example.

Answer 1

You could have a look at how it is done in the Nicks pallet.

In short, you are first filling the storage with existing runtime calls and then checking the storage whether these calls succeeded.