wrote a function and its tests to count specific letters in a string

solutions/count_specific_string_letters.py

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+""" 
+A function that counts a specific string letters in a sentence using the count method.
+
+function contents -
+    count_string = a function that counts the occurrence of a specific letter in a given sentence or phrase.
+
+ created on 07 Jan 2025
+ @author: Hope Udoh
+
+
+"""
+
+def count_string(sentence:str, letters:str) -> str:
+    """
+    This function counts the occurrence of a specific letter in a given sentence.
+
+    Parameters:
+    sentence (str): The input sentence where the letter count will be performed.
+    letters (str): The specific letter to count its occurrence in the sentence.
+
+    Returns:
+    str: A string indicating the count of the specific letter in the sentence.
+
+    Raises:
+        AssertionError: if the argument(letters) is not a string
+        AssertionError: if the argument(sentence) is not a string
+        ValueError: If the letters parameter is an empty string.
+
+    Example 1:
+    >>> count_string("hello", "l")
+    'the letter 'l' appears 2 times'
+
+    Example 2:
+    >>> count_string("I love pineapples too much", "t"))
+    'the letter 't' appears 1 times'
+
+
+    """
+    if not letters:
+      raise ValueError("The letter to count must not be empty.")
+
+    specific_letter_count = sentence.count(letters)
+    return (f"The letter '{letters}' appears {specific_letter_count} times")
+
+
+
+

solutions/tests/test_count_specific_string_letters.py

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+import unittest
+from solutions.count_specific_string_letters import count_string
+
+
+"""
+Test module for the count_string function.
+This file includes unittest to verify the correctness of the count_string function.
+It tests the function with standard cases and edge cases.
+Test categories:
+    - Standard cases: Test that the function correctly counts a single occurrence of a letter.
+    - Edge cases: empty sentence and empty letter
+    - Large input: lists with a large range of strings (e.g., thousands)
+Created on: 07 January 2025
+Author: Hope Udoh
+"""
+
+class TestCountString(unittest.TestCase):
+    """
+    Test suite for the count_string function.
+    """
+
+    #Standard Cases
+    def test_single_occurrence(self):
+        """
+        Standard Case: Test that the function correctly counts a single occurrence of a letter.
+
+        Example:
+        >>> count_string("hello", "e")
+        'The letter 'e' appears 1 times'
+        """
+        self.assertEqual(count_string("hello", "e"), "The letter 'e' appears 1 times")
+
+    def test_multiple_occurrences(self):
+        """
+        Standard Case: Test that the function correctly counts multiple occurrences of a letter.
+
+        Example:
+        >>> count_string("banana", "a")
+        'The letter 'a' appears 3 times'
+        """
+        self.assertEqual(count_string("banana", "a"), "The letter 'a' appears 3 times")
+
+    def test_no_occurrence(self):
+        """
+        Standard Case: Test that the function returns zero when the letter does not occur.
+
+        Example:
+        >>> count_string("world", "x")
+        'The letter 'x' appears 0 times'
+        """
+        self.assertEqual(count_string("world", "x"), "The letter 'x' appears 0 times")
+
+    # Edge Cases
+    def test_empty_sentence(self):
+        """
+        Edge Case: Test that the function returns zero when the sentence is empty.
+
+        Example:
+        >>> count_string("", "a")
+        'The letter 'a' appears 0 times'
+        """
+        self.assertEqual(count_string("", "a"), "The letter 'a' appears 0 times")
+
+    def test_empty_letter(self):
+        """
+        Edge Case: Test that the function raises a ValueError when the letter is empty.
+
+        Raises:
+            ValueError: If the letter is an empty string.
+
+        Example:
+        >>> count_string("hello", "")
+        Traceback (most recent call last):
+        ...
+        ValueError: The letter to count must not be empty.
+        """
+        with self.assertRaises(ValueError):
+            count_string("hello", "")
+
+    # Large Input Cases
+    def test_large_input(self):
+        """
+        Large Input Case: Test the function with a large input sentence.
+
+        Example:
+        >>> count_string("a" * 10000, "a")
+        'The letter 'a' appears 10000 times'
+        """
+        self.assertEqual(count_string("a" * 10000, "a"), "The letter 'a' appears 10000 times")
+if __name__ == "__main__":
+    unittest.main()
+
+
+
+