Logic Tests

In this section we’ll test previously written ERC-20 logic.

Test Module

Add new file for tests at logic/src/tests.rs and include this module at the top of logic/src/lib.rs.

mod tests;

Write simple test to verify it works.

// logic/src/tests.rs

fn my_test() {
    assert_eq!(1, 1);

And run it.

$ cargo test -p logic

running 1 test
test tests::my_test ... ok

Test Token Implementation

Testing traits requires us to implement it first. Let’s create a test token struct.

// logic/src/tests.rs

use std::collections::HashMap;

type Amount = u64;
type Address = u8;
type AddressPair = (Address, Address);

struct Token {
    total_supply_count: Amount,
    balances: HashMap<Address, Amount>,
    allowance: HashMap<AddressPair, Amount>,

impl Token {
    fn new() -> Token {
        Token {
            total_supply_count: 0,
            balances: HashMap::new(),
            allowance: HashMap::new(),

The Token struct can store all the data ERC-20 tokens require, so it’s possible to implement ERC20Trait on top of it.

// logic/src/tests.rs

impl ERC20Trait<Amount, Address> for Token {
    fn read_balance(&mut self, address: &Address) -> Option<Amount> {

    fn save_balance(&mut self, address: &Address, balance: Amount) {
        self.balances.insert(*address, balance);

    fn read_total_supply(&mut self) -> Option<Amount> {

    fn save_total_supply(&mut self, new_total_supply: Amount) {
        self.total_supply_count = new_total_supply;

    fn read_allowance(&mut self, owner: &Address, spender: &Address) -> Option<Amount> {
        self.allowance.get(&(*owner, *spender)).cloned()

    fn save_allowance(&mut self, owner: &Address, spender: &Address, amount: Amount) {
        self.allowance.insert((*owner, *spender), amount);

Unit Tests

All ERC-20 operations are account-based, so it’s handy to have a few accounts already defined.

const ADDRESS_1: Address = 1;
const ADDRESS_2: Address = 2;
const ADDRESS_3: Address = 3;

Example of how to test transfer function.

fn test_transfer() {
    let mut token = Token::new();
    token.mint(&ADDRESS_1, 10);
    let transfer_result = token.transfer(&ADDRESS_1, &ADDRESS_2, 3);
    assert_eq!(token.balance_of(&ADDRESS_1), 7);
    assert_eq!(token.balance_of(&ADDRESS_2), 3);
    assert_eq!(token.total_supply(), 10);

Rest of the tests are found on Github: tests.rs.