Why is the AccountId of a contract always 1 when unit testing?

Question

I've been building unit tests in ink and have come across a strange issue. If I instantiate a contract multiple times, the account id is always the same. I thought the account id is the address of the contract, hence should be different between two contract instantiations.

Code:

let c1 = MyContract::new();
println!("{:?}", c1.env().account_id()); // prints AccountId([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1])

let c2 = MyContract::new();
println!("{:?}", c2.env().account_id()); // prints AccountId([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1])

let c3 = MyContract::new();
println!("{:?}", c3.env().account_id()); // prints AccountId([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1])

Shouldn't the account id be different?

Answer 1

Off-chain environment used in the unit testing is just a mock environment so there aren't any dedicated mapping created b/w addresses & contracts. Latter is just an object with some associated values (in context of ink! off-chain engine). So multiple contracts can have the same address.

You need to manually set the callee before initialising a contract otherwise your contract address will be same as the last set callee (which is by default [1;32]). Below is a sample implementation on how to do it.

let contract_addr: AccountId = AccountId::from([0xFF as u8; 32]);  
set_callee::<DefaultEnvironment>(contract_addr);
let mut contract = MyContract::default();

assert_eq!(contract.env().account_id(), contract_addr); // true