diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 00000000..55b033e9
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1 @@
+pytest
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diff --git a/src/array_utils.py b/src/array_utils.py
new file mode 100644
index 00000000..ee93261b
--- /dev/null
+++ b/src/array_utils.py
@@ -0,0 +1,29 @@
+from typing import List, Union, Any
+
+def flatten(arr: Union[List[Any], Any]) -> List[Any]:
+    """
+    Recursively flatten a nested list into a single-level list.
+    
+    Args:
+        arr (Union[List[Any], Any]): Input list that may contain nested lists.
+    
+    Returns:
+        List[Any]: A flattened list with all nested elements extracted.
+    
+    Raises:
+        TypeError: If input is not a list and cannot be flattened.
+    """
+    # Base case: if input is not a list, return it as a single-element list
+    if not isinstance(arr, list):
+        return [arr]
+    
+    # Recursive flattening
+    flattened = []
+    for item in arr:
+        # Recursively flatten each item
+        if isinstance(item, list):
+            flattened.extend(flatten(item))
+        else:
+            flattened.append(item)
+    
+    return flattened
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diff --git a/src/string_reversal.py b/src/string_reversal.py
new file mode 100644
index 00000000..2e378e67
--- /dev/null
+++ b/src/string_reversal.py
@@ -0,0 +1,34 @@
+def reverse_string(input_string):
+    """
+    Reverse the given string using a manual character-by-character approach.
+
+    Args:
+        input_string (str): The string to be reversed.
+
+    Returns:
+        str: The reversed string.
+
+    Raises:
+        TypeError: If the input is not a string.
+    """
+    # Check if input is a string
+    if not isinstance(input_string, str):
+        raise TypeError("Input must be a string")
+    
+    # Convert string to list of characters
+    chars = list(input_string)
+    
+    # Reverse the list of characters manually
+    left = 0
+    right = len(chars) - 1
+    
+    while left < right:
+        # Swap characters
+        chars[left], chars[right] = chars[right], chars[left]
+        
+        # Move towards the center
+        left += 1
+        right -= 1
+    
+    # Convert back to string and return
+    return ''.join(chars)
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diff --git a/tests/test_array_utils.py b/tests/test_array_utils.py
new file mode 100644
index 00000000..49602f39
--- /dev/null
+++ b/tests/test_array_utils.py
@@ -0,0 +1,34 @@
+import pytest
+from src.array_utils import flatten
+
+def test_flatten_simple_list():
+    """Test flattening a simple list"""
+    assert flatten([1, 2, 3]) == [1, 2, 3]
+
+def test_flatten_nested_list():
+    """Test flattening a list with one level of nesting"""
+    assert flatten([1, [2, 3], 4]) == [1, 2, 3, 4]
+
+def test_flatten_deeply_nested_list():
+    """Test flattening a list with multiple levels of nesting"""
+    assert flatten([1, [2, [3, 4]], 5]) == [1, 2, 3, 4, 5]
+
+def test_flatten_complex_nested_list():
+    """Test flattening a more complex nested list"""
+    assert flatten([1, [2, [3, [4, 5]]], 6]) == [1, 2, 3, 4, 5, 6]
+
+def test_flatten_empty_list():
+    """Test flattening an empty list"""
+    assert flatten([]) == []
+
+def test_flatten_non_list_single_element():
+    """Test flattening a single non-list element"""
+    assert flatten(42) == [42]
+
+def test_flatten_mixed_types():
+    """Test flattening a list with mixed types of nested elements"""
+    assert flatten([1, [2, 'three'], [4, [5, None]]]) == [1, 2, 'three', 4, 5, None]
+
+def test_nested_empty_lists():
+    """Test flattening lists containing empty lists"""
+    assert flatten([1, [], [2, []], 3]) == [1, 2, 3]
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diff --git a/tests/test_string_reversal.py b/tests/test_string_reversal.py
new file mode 100644
index 00000000..da8abb11
--- /dev/null
+++ b/tests/test_string_reversal.py
@@ -0,0 +1,30 @@
+import pytest
+from src.string_reversal import reverse_string
+
+def test_reverse_string_basic():
+    """Test basic string reversal."""
+    assert reverse_string("hello") == "olleh"
+    assert reverse_string("python") == "nohtyp"
+
+def test_reverse_string_empty():
+    """Test reversal of an empty string."""
+    assert reverse_string("") == ""
+
+def test_reverse_string_special_chars():
+    """Test reversal of string with special characters."""
+    assert reverse_string("a!b@c#") == "#c@b!a"
+
+def test_reverse_string_unicode():
+    """Test reversal of unicode string."""
+    assert reverse_string("café") == "éfac"
+
+def test_reverse_string_invalid_input():
+    """Test that TypeError is raised for non-string inputs."""
+    with pytest.raises(TypeError, match="Input must be a string"):
+        reverse_string(123)
+    
+    with pytest.raises(TypeError, match="Input must be a string"):
+        reverse_string(None)
+    
+    with pytest.raises(TypeError, match="Input must be a string"):
+        reverse_string(["list"])
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