public void AccountUnsubscribeFromCommissionFail() { //Arrange CommissionAccount acc = new CommissionAccount("123", 10, Currency.AUD); //Assert AccountManager nothing = null; var ex = Assert.Throws <ArgumentNullException>(() => acc.UnsubscribeFromCommission(nothing)); Assert.AreEqual($"{ExceptionMessages.AccountUnsubscribeNullParam() + Environment.NewLine}Parameter name: accountManager", ex.Message); }