nosetests assertGreaterEqual

I have written a unit test for a function but i cant seem to get what the error means.

Here's the app class

class ShoppingList(object):

    cart = {}  # A dictionary to hold item_name:price as key:value 
    balance = 0
    budget_amount = 0  # one wouldn't want to shop for more than is available
    
    def __init__(self, budget_amount):
        self.budget_amount = budget_amount        
    
    # a method to add items to the cart dictionary
    def addItem(self, item_name, price, quantity):
        # declare argument types and check they are use correctly
        number_types = ( int, float, complex)
    
        if isinstance(price, number_types) and isinstance(quantity, number_types) and isinstance(item_name, str):
            self.cart[item_name] = price
    
            total_cost = self.calculatePrice(price, quantity)
    
            self.balance = self.budget_amount - total_cost
        else:
            raise ValueError
    
    # a method to calculate total cost
    def calculatePrice(self, price, quantity):
    
        total_amount = price * quantity
        #check total doesnt exceed balance we have
        if total_amount > self.balance:
            return("That amount is more than what we have")
    
        return total_amount

And the unit tests that i put down are described below.

import unittest
from app.shoppinglist import ShoppingList

# a class to contain test cases for the shopping list

class ShoppingListTest( unittest.TestCase ):

    def setUp(self):
        budget_amount = 500
        self.shoppingList = ShoppingList(budget_amount)

    # method to test value types in addItem
    def test_addItem_method_returns_error_for_nonInt(self):
        self.assertRaises(ValueError, self.shoppingList.addItem, 1, "one", "thirty")

    # method to check if quantity arg is not a number
    def test_addItem_method_returns_error_for_quantityArg_string(self):
        self.assertRaises( ValueError, self.shoppingList.addItem, "rice", "four", 400)

    # method to check if price arg is not a number
    def test_addItem_method_returns_error_for_priceArg_string(self):
        self.assertRaises( ValueError, self.shoppingList.addItem, "Water", 4, "hundred")

    # check if calculatePrice raises an error if total cost exceeds budget cost
    def test_calculatePrice_returns_err_for_exceedingBudget(self):
        result = self.shoppingList.calculatePrice( 2, 150)
        self.assertGreaterEqual(self.shoppingList.balance, result)

When i run the tests calculatePrice always returns and error that type error '>=' not supported between instance of int and str. What i want to achieve is make sure that the total_price in calculatePrice doesnt exceed the balance. If it does raise an error to notify user

I will appreciate any help from anyone. Thank you

Here's the problem, if you cannot buy it, the total_amount should be 0, not a string. Due to calculatePrice should always return number

def calculatePrice(self, price, quantity):

    total_amount = price * quantity
    #check total doesnt exceed balance we have
    if total_amount > self.balance:
        print("That amount is more than what we have")
        return 0
    return total_amount