diff --git a/__init__.py b/__init__.py
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diff --git a/requirements.txt b/requirements.txt
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diff --git a/solutions/basic_calculator/__init__.py b/solutions/basic_calculator/__init__.py
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diff --git a/solutions/basic_calculator/calculate.py b/solutions/basic_calculator/calculate.py
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+"""
+A module for performing basic arithmetic operations: addition, subtraction,
+multiplication, and division.
+
+Module contents:
+    - calculate: Performs the specified arithmetic operation on two numbers
+
+Created on 28/12/2024
+Author: Ana Isabel Murillo
+"""
+
+
+def calculate(operation: str, num1: float, num2: float) -> float:
+    """Performs the specified arithmetic operation on two numbers.
+
+    Parameters:
+        operation: str, the operation to perform
+        ('add', 'subtract', 'multiply', 'divide')
+        num1: float, the first number
+        num2: float, the second number
+
+    Returns -> float: the result of the arithmetic operation
+
+    Raises:
+        ValueError: if the operation is invalid or division by zero occurs
+
+    Examples:
+        >>> calculate('add', 5, 3)
+        8.0
+        >>> calculate('subtract', 10, 4)
+        6.0
+        >>> calculate('multiply', 7, 3)
+        21.0
+        >>> calculate('divide', 9, 3)
+        3.0
+        >>> calculate('divide', 5, 0)
+        Traceback (most recent call last):
+            ...
+        ValueError: Cannot divide by zero.
+    """
+    if operation == "add":
+        return num1 + num2
+    elif operation == "subtract":
+        return num1 - num2
+    elif operation == "multiply":
+        return num1 * num2
+    elif operation == "divide":
+        if num2 == 0:
+            raise ValueError("Cannot divide by zero.")
+        return num1 / num2
+    else:
+        raise ValueError(
+            f"Invalid operation '{operation}'. Valid operations are: "
+            "add, subtract, multiply, divide."
+        )
diff --git a/solutions/tests/test_basic_calculator.py b/solutions/tests/test_basic_calculator.py
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+"""
+Test module for basic calculator.
+
+Test categories:
+    - Standard cases: addition, subtraction, multiplication, and division
+    - Edge cases: division by zero, invalid operations
+    - Defensive tests: ensure proper exceptions are raised for invalid inputs
+
+Created on 2024-12-29
+Author: Ana Isabel Murillo
+"""
+
+from solutions.basic_calculator.calculate import calculate
+
+import unittest
+
+
+class TestCalculate(unittest.TestCase):
+    """Test suite for the calculate function."""
+
+    def test_addition_positive_numbers(self):
+        """It should correctly add two positive numbers."""
+        self.assertEqual(calculate("add", 5, 3), 8.0)
+
+    def test_addition_negative_numbers(self):
+        """It should correctly add two negative numbers."""
+        self.assertEqual(calculate("add", -5, -3), -8.0)
+
+    def test_addition_zero(self):
+        """It should correctly add zero to a number."""
+        self.assertEqual(calculate("add", 0, 5), 5.0)
+
+    def test_subtraction_positive_numbers(self):
+        """It should correctly subtract two positive numbers."""
+        self.assertEqual(calculate("subtract", 10, 4), 6.0)
+
+    def test_subtraction_negative_numbers(self):
+        """It should correctly subtract two negative numbers."""
+        self.assertEqual(calculate("subtract", -5, -5), 0.0)
+
+    def test_subtraction_zero(self):
+        """It should correctly subtract a number from zero."""
+        self.assertEqual(calculate("subtract", 0, 5), -5.0)
+
+    def test_multiplication_positive_numbers(self):
+        """It should correctly multiply two positive numbers."""
+        self.assertEqual(calculate("multiply", 7, 3), 21.0)
+
+    def test_multiplication_negative_numbers(self):
+        """It should correctly multiply a negative and a positive number."""
+        self.assertEqual(calculate("multiply", -2, 3), -6.0)
+
+    def test_multiplication_with_zero(self):
+        """It should return zero when multiplying by zero."""
+        self.assertEqual(calculate("multiply", 0, 10), 0.0)
+
+    def test_division_positive_numbers(self):
+        """It should correctly divide two positive numbers."""
+        self.assertEqual(calculate("divide", 9, 3), 3.0)
+
+    def test_division_negative_numbers(self):
+        """It should correctly divide a negative and a positive number."""
+        self.assertEqual(calculate("divide", -6, 3), -2.0)
+
+    def test_division_result_with_float(self):
+        """It should correctly handle division resulting in a float."""
+        self.assertAlmostEqual(calculate("divide", 7, 2), 3.5)
+
+    def test_division_by_zero(self):
+        """It should raise a ValueError when attempting to divide by zero."""
+        with self.assertRaises(ValueError) as context:
+            calculate("divide", 5, 0)
+        self.assertEqual(str(context.exception), "Cannot divide by zero.")
+
+    def test_invalid_operation(self):
+        """It should raise a ValueError for an invalid operation."""
+        with self.assertRaises(ValueError) as context:
+            calculate("invalid_op", 5, 3)
+        self.assertIn("Invalid operation", str(context.exception))