Step 5

In this step, we will start using #[pallet::genesis] features.

• Step 5
  • information Points
  • In the code
  • Interaction

information Points

In the code

• Let's look at our test_state(). Not so pretty. Also, when we launched a node, it had no initial balance when we ran a node. Can we do better? yes.
• start by adding #[pallet::genesis_config]. The fields of this struct are the pieces of information that your pallet expects to receive from someone (eg. a genesis chain specification). For our case, we expect to get a list of accounts and balances.
• Then, #[pallet::genesis_build] defines what your pallet should do with that. We will insert into Balances, and update TotalIssuance.
• This function is called before your chain even launches. So if there is anything wrong, we simply panic and no need for nicer error handling.

Later on you will learn about avoiding panics in the runtime. In general, you should not panic.

• GenesisConfig is required to have a Default. We are simply happy with an empty vector for that, so we derive it.

Note that frame::derive::DefaultNoBound is simply preventing clashes with <T: Config>. If the struct hadn't had <T: Config>, derive(Default) would have been just enough.

• Then, to using this in our test setup.
• First, we explore the approach where we create the GenesisConfig of each pallet, then amalgamate them in RuntimeGenesisConfig (this is generated by construct_runtime) and use that as our initial state. This is demonstrate it test_state_new.
• we demonstrate an alternative syntax for that in test_state_new_2 which is semantically the same. We leave it up to you to figure out why!
• Finally, we create a builder pattern to do the same. This is a very common practice in Rust and is well-explained externally.
• Other than being more ergonomic, the benefit of our builder pattern is that it will flexibly support adding more accounts at genesis.
• We add a new test ext_builder_works to demonstrate this.
• Moreover, it allows some additional code to be executed after each tests. We add some code that ensures total issuance is always checked, now we get even more coverage.
• We add a new test duplicate_genesis_fails to demonstrate the check we put into place.
• We Migrate all existing tests to use the ExtBuilder.

Interaction

TODO: Finally, we can add a few initial balances in the cli's chain spec as well. given the unclear status of the node for now I won't cover this, but the code in staging is demonstrating what needs to be done.