Simulating calls

Sometimes you want to simulate a call to a contract without changing the state of the blockchain. This can be achieved by calling .simulate instead of .call and passing in the desired execution context:

• .simulate(Execution::realistic()) simulates the transaction in a manner that closely resembles a real call. You need a wallet with base assets to cover the transaction cost, even though no funds will be consumed. This is useful for validating that a real call would succeed if made at that moment. It allows you to debug issues with your contract without spending gas.

        // you would mint 100 coins if the transaction wasn't simulated
        let counter = contract_methods
            .mint_coins(100)
            .simulate(Execution::realistic())
            .await?;

• .simulate(Execution::state_read_only()) disables many validations, adds fake gas, extra variable outputs, blank witnesses, etc., enabling you to read state even with an account that has no funds.

            // you don't need any funds to read state
            let balance = contract_methods
                .get_balance(contract_id, AssetId::zeroed())
                .simulate(Execution::state_read_only())
                .await?
                .value;

If the node supports historical execution (the node is using rocksdb and the historical_execution flag has been set), then both execution types can be chained with at_height to simulate the call at a specific block height.

            let balance = contract_methods
                .get_balance(contract_id, AssetId::zeroed())
                .simulate(Execution::state_read_only().at_height(block_height))
                .await?
                .value;