Stricten assertions on test_deposit

[jpcenteno]

Address these comments by @mpaulucci.

Take this as a reference:

        assert_eq!(
            l2_balance_after_withdraw,
            l2_balance_before
                - (amount_to_withdraw + tx_receipt.effective_gas_price.unwrap() * tx_receipt.gas_used.unwrap()),
            "Check that L2 balance inmediately after withdrawal has decreased by the used gas and amount"
        );