Test authorized contract invocations

A contract's test functions can be used as a way to ensure the authorization is indeed carried out the way a developer intends. A simple example can be found in the auth example contract. (In the following code block, some code has been omitted for brevity.)

#[test]
fn test() {
    let env = Env::default();
    env.mock_all_auths();

    assert_eq!(client.increment(&user_1, &5), 5);
    // Verify that the user indeed had to authorize a call of `increment` with
    // the expected arguments:
    assert_eq!(
        env.auths(),
        std::vec![(
            // Address for which authorization check is performed
            user_1.clone(),
            // Invocation tree that needs to be authorized
            AuthorizedInvocation {
                // Function that is authorized. Can be a contract function or
                // a host function that requires authorization.
                function: AuthorizedFunction::Contract((
                    // Address of the called contract
                    contract_id.clone(),
                    // Name of the called function
                    symbol_short!("increment"),
                    // Arguments used to call `increment` (converted to the
                    // env-managed vector via `into_val`)
                    (user_1.clone(), 5_u32).into_val(&env),
                )),
                // The contract doesn't call any other contracts that require
                // authorization,
                sub_invocations: std::vec![]
            }
        )]
    )
}