diff --git a/src/array_flattener.py b/src/array_flattener.py
new file mode 100644
index 00000000..bc81a6d7
--- /dev/null
+++ b/src/array_flattener.py
@@ -0,0 +1,34 @@
+from typing import List, Union
+
+def flatten_array(arr: List[Union[int, List]]) -> List[int]:
+    """
+    Flatten a nested list of integers to a single-level list.
+    
+    Args:
+        arr (List[Union[int, List]]): A potentially nested list of integers.
+    
+    Returns:
+        List[int]: A flattened list of integers.
+    
+    Raises:
+        TypeError: If the input contains non-integer or non-list elements.
+    
+    Examples:
+        >>> flatten_array([1, [2, 3], 4])
+        [1, 2, 3, 4]
+        >>> flatten_array([1, [2, [3, 4]], 5])
+        [1, 2, 3, 4, 5]
+    """
+    result = []
+    
+    def _recursive_flatten(item):
+        if isinstance(item, int):
+            result.append(item)
+        elif isinstance(item, list):
+            for sub_item in item:
+                _recursive_flatten(sub_item)
+        else:
+            raise TypeError(f"Invalid element type: {type(item)}. Only integers and lists are allowed.")
+    
+    _recursive_flatten(arr)
+    return result
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diff --git a/src/string_reversal.py b/src/string_reversal.py
new file mode 100644
index 00000000..a1331ec5
--- /dev/null
+++ b/src/string_reversal.py
@@ -0,0 +1,36 @@
+def reverse_string(input_string: str) -> str:
+    """
+    Reverse the given input string manually.
+    
+    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")
+    
+    # Handle empty string case
+    if len(input_string) <= 1:
+        return input_string
+    
+    # Convert string to list of characters for manual reversal
+    chars = list(input_string)
+    
+    # Manual reversal using two-pointer technique
+    left, right = 0, len(chars) - 1
+    while left < right:
+        # Swap characters
+        chars[left], chars[right] = chars[right], chars[left]
+        
+        # Move pointers
+        left += 1
+        right -= 1
+    
+    # Convert back to string and return
+    return ''.join(chars)
\ No newline at end of file
diff --git a/tests/test_array_flattener.py b/tests/test_array_flattener.py
new file mode 100644
index 00000000..2c6938c5
--- /dev/null
+++ b/tests/test_array_flattener.py
@@ -0,0 +1,28 @@
+import pytest
+from src.array_flattener import flatten_array
+
+def test_flatten_simple_nested_list():
+    input_list = [1, [2, 3], 4]
+    assert flatten_array(input_list) == [1, 2, 3, 4]
+
+def test_flatten_deeply_nested_list():
+    input_list = [1, [2, [3, 4]], 5]
+    assert flatten_array(input_list) == [1, 2, 3, 4, 5]
+
+def test_flatten_multiple_level_nesting():
+    input_list = [1, [2, [3, [4, 5]]], 6]
+    assert flatten_array(input_list) == [1, 2, 3, 4, 5, 6]
+
+def test_flatten_empty_list():
+    assert flatten_array([]) == []
+
+def test_flatten_single_integer():
+    assert flatten_array(5) == [5]
+
+def test_invalid_element_type():
+    with pytest.raises(TypeError, match="Invalid element type"):
+        flatten_array([1, 2, "three"])
+
+def test_mixed_nested_lists():
+    input_list = [1, [2, 3, [4, [5]]], 6]
+    assert flatten_array(input_list) == [1, 2, 3, 4, 5, 6]
\ No newline at end of file
diff --git a/tests/test_string_reversal.py b/tests/test_string_reversal.py
new file mode 100644
index 00000000..4f6df057
--- /dev/null
+++ b/tests/test_string_reversal.py
@@ -0,0 +1,38 @@
+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_single_char():
+    """Test reversal of a single character."""
+    assert reverse_string("a") == "a"
+
+def test_reverse_string_with_spaces():
+    """Test reversal of string with spaces."""
+    assert reverse_string("hello world") == "dlrow olleh"
+
+def test_reverse_string_with_special_chars():
+    """Test reversal of string with special characters."""
+    assert reverse_string("a1b2c3!@#") == "#@!3c2b1a"
+
+def test_reverse_string_mixed_characters():
+    """Test reversal of string with mixed character types."""
+    assert reverse_string("Hello, World! 123") == "321 !dlroW ,olleH"
+
+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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