diff --git a/solutions/sum_proper_divisors.py b/solutions/sum_proper_divisors.py
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+++ b/solutions/sum_proper_divisors.py
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+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+A module for calculating the sum of proper divisors of a number.
+
+Module contents:
+    - sum_proper_divisors: calculates the sum of proper divisors of a given number.
+
+Created on Jan 08 2025
+@author: Ibrahim Elmisbah
+"""
+
+
+def sum_proper_divisors(n: int) -> int:
+    """Calculate the sum of proper divisors of a number.
+
+    A proper divisor of a number is a divisor that is less than the number itself.
+
+    Parameters:
+        n: int, the input number (must be positive)
+
+    Returns -> int: the sum of proper divisors of the number
+
+    Raises:
+        AssertionError: if the argument is not a positive integer
+
+    >>> sum_proper_divisors(6)
+    6
+    >>> sum_proper_divisors(10)
+    8
+    >>> sum_proper_divisors(1)
+    0
+    """
+    assert isinstance(n, int), "Input must be an integer"
+    assert n > 0, "Input must be a positive integer"
+
+    # Initialize the sum of divisors
+    total = 0
+
+    # Check all possible divisors from 1 to n // 2
+    for i in range(1, n // 2 + 1):
+        # If 'i' divides 'n' without a remainder, it is a divisor
+        if n % i == 0:
+            total += i  # Add 'i' to the total sum of proper divisors
+
+    return total
diff --git a/solutions/tests/test_sum_proper_divisors.py b/solutions/tests/test_sum_proper_divisors.py
new file mode 100644
index 000000000..566bb2c59
--- /dev/null
+++ b/solutions/tests/test_sum_proper_divisors.py
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+import unittest
+
+from ..sum_proper_divisors import sum_proper_divisors
+
+
+class TestSumProperDivisors(unittest.TestCase):
+    """Tests for the sum_proper_divisors function."""
+
+    def test_small_number(self):
+        """It should return the correct sum for a small number."""
+        actual = sum_proper_divisors(6)
+        expected = 6
+        self.assertEqual(actual, expected)
+
+    def test_prime_number(self):
+        """It should return 1 for a prime number."""
+        actual = sum_proper_divisors(7)
+        expected = 1
+        self.assertEqual(actual, expected)
+
+    def test_one(self):
+        """It should return 0 for the number 1."""
+        actual = sum_proper_divisors(1)
+        expected = 0
+        self.assertEqual(actual, expected)
+
+    def test_large_number(self):
+        """It should return the correct sum for a large number."""
+        actual = sum_proper_divisors(28)
+        expected = 28
+        self.assertEqual(actual, expected)
+
+    def test_non_integer(self):
+        """It should raise AssertionError for non-integer input."""
+        with self.assertRaises(AssertionError):
+            sum_proper_divisors(10.5)
+
+    def test_negative_number(self):
+        """It should raise AssertionError for a negative number."""
+        with self.assertRaises(AssertionError):
+            sum_proper_divisors(-5)
+
+    def test_zero(self):
+        """It should raise AssertionError for zero input."""
+        with self.assertRaises(AssertionError):
+            sum_proper_divisors(0)