Introduce custom exception for handling negative numbers

Author: balazs-domonkos-epam

src/coding_task/app.py

@@ -1,9 +1,11 @@
-from coding_task.string_calculator import calculate_sum
+from coding_task.string_calculator import *
 
 
 def run_app():
     user_input = input("Enter delimited numbers to add: ")
     try:
         print("Total sum: ", calculate_sum(user_input))
+    except NegativeNumbersNotSupportedException as ex:
+        print("Error: Negative numbers are not supported!")
     except Exception as ex:
         print("An unexpected error occurred: ", str(ex))

src/coding_task/string_calculator.py

@@ -2,12 +2,16 @@
 
 SUPPORTED_DELIMITERS = r'[\s,;:\_]'
 MAX_NUMBER = 100
-MESSAGE_NEGATIVE_NUMBERS_NOT_SUPPORTED = "Negative numbers are not supported!"
+
+
+class NegativeNumbersNotSupportedException(Exception):
+    def __init__(self):
+        pass
 
 
 def __validate(number):
     if number < 0:
-        raise ValueError(MESSAGE_NEGATIVE_NUMBERS_NOT_SUPPORTED)
+        raise NegativeNumbersNotSupportedException
     return number
 
 

test/test_string_calculator.py

@@ -1,6 +1,7 @@
 import pytest
 
 from coding_task.string_calculator import calculate_sum
+from coding_task.string_calculator import NegativeNumbersNotSupportedException
 
 test_cases_for_sum_calculation = [
     ("5", 5),
@@ -97,8 +98,7 @@ def test_ignore_numbers_over_100(input_string, expected):
 
 def test_calculates_sum_should_throw_exception_when_negative_number_is_provided():
     """
-    Test 'calculate_sum()' to throw 'ValueError' exception when negative numbers provided
+    Test 'calculate_sum()' to throw 'NegativeNumbersNotSupportedException' exception when negative numbers are provided
     """
-    with pytest.raises(ValueError) as exception:
+    with pytest.raises(NegativeNumbersNotSupportedException):
         calculate_sum("1,2,-3")
-    assert str(exception.value) == "Negative numbers are not supported!"