diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b48e2fc..b9256f4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -2,9 +2,9 @@ name: CI
 
 on:
   push:
-    branches: [main, dev]
+    branches: [main, master, dev]
   pull_request:
-    branches: [main, dev]
+    branches: [main, master, dev]
 
 jobs:
   lint-and-type-check:
diff --git a/calculator.py b/calculator.py
new file mode 100644
index 0000000..9ea0d19
--- /dev/null
+++ b/calculator.py
@@ -0,0 +1,52 @@
+"""
+A simple calculator module for testing CI/CD workflows.
+"""
+from typing import Union
+
+
+class Calculator:
+    """Basic calculator with arithmetic operations."""
+
+    @staticmethod
+    def add(a: Union[int, float], b: Union[int, float]) -> Union[int, float]:
+        """Add two numbers."""
+        return a + b
+
+    @staticmethod
+    def subtract(a: Union[int, float], b: Union[int, float]) -> Union[int, float]:
+        """Subtract b from a."""
+        return a - b
+
+    @staticmethod
+    def multiply(a: Union[int, float], b: Union[int, float]) -> Union[int, float]:
+        """Multiply two numbers."""
+        return a * b
+
+    @staticmethod
+    def divide(a: Union[int, float], b: Union[int, float]) -> float:
+        """Divide a by b."""
+        if b == 0:
+            raise ValueError("Cannot divide by zero")
+        return a / b
+
+    @staticmethod
+    def power(a: Union[int, float], b: Union[int, float]) -> Union[int, float]:
+        """Raise a to the power of b."""
+        return a**b
+
+
+def main() -> None:
+    """Demo usage of the calculator."""
+    calc = Calculator()
+
+    print("Calculator Demo")
+    print("=" * 40)
+    print(f"5 + 3 = {calc.add(5, 3)}")
+    print(f"10 - 4 = {calc.subtract(10, 4)}")
+    print(f"6 * 7 = {calc.multiply(6, 7)}")
+    print(f"15 / 3 = {calc.divide(15, 3)}")
+    print(f"2 ^ 8 = {calc.power(2, 8)}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/requirements.txt b/requirements.txt
index f1ae579..d1480a8 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,8 @@
-# Add your Python dependencies here
-# Example:
-# requests>=2.28.0
-# flask>=2.3.0
+# Testing dependencies
+pytest>=7.4.0
+pytest-cov>=4.1.0
+
+# Code quality tools
+black>=23.0.0
+pylint>=3.0.0
+mypy>=1.5.0
diff --git a/string_utils.py b/string_utils.py
new file mode 100644
index 0000000..5ba8dfc
--- /dev/null
+++ b/string_utils.py
@@ -0,0 +1,32 @@
+"""
+String utility functions for testing CI/CD workflows.
+"""
+
+
+def reverse_string(text: str) -> str:
+    """Reverse a string."""
+    return text[::-1]
+
+
+def is_palindrome(text: str) -> bool:
+    """Check if a string is a palindrome."""
+    cleaned = "".join(c.lower() for c in text if c.isalnum())
+    return cleaned == cleaned[::-1]
+
+
+def count_vowels(text: str) -> int:
+    """Count the number of vowels in a string."""
+    vowels = "aeiouAEIOU"
+    return sum(1 for char in text if char in vowels)
+
+
+def title_case(text: str) -> str:
+    """Convert string to title case."""
+    return " ".join(word.capitalize() for word in text.split())
+
+
+def truncate(text: str, max_length: int, suffix: str = "...") -> str:
+    """Truncate string to max length with optional suffix."""
+    if len(text) <= max_length:
+        return text
+    return text[: max_length - len(suffix)] + suffix
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..46816dd
--- /dev/null
+++ b/tests/__init__.py
@@ -0,0 +1 @@
+"""Tests package."""
diff --git a/tests/test_calculator.py b/tests/test_calculator.py
new file mode 100644
index 0000000..35fcde7
--- /dev/null
+++ b/tests/test_calculator.py
@@ -0,0 +1,56 @@
+"""
+Tests for the calculator module.
+"""
+import pytest
+from calculator import Calculator
+
+
+class TestCalculator:
+    """Test suite for Calculator class."""
+
+    def test_add_positive_numbers(self):
+        """Test addition of positive numbers."""
+        assert Calculator.add(5, 3) == 8
+        assert Calculator.add(10, 20) == 30
+
+    def test_add_negative_numbers(self):
+        """Test addition with negative numbers."""
+        assert Calculator.add(-5, -3) == -8
+        assert Calculator.add(-10, 5) == -5
+
+    def test_subtract(self):
+        """Test subtraction."""
+        assert Calculator.subtract(10, 3) == 7
+        assert Calculator.subtract(5, 10) == -5
+
+    def test_multiply(self):
+        """Test multiplication."""
+        assert Calculator.multiply(5, 3) == 15
+        assert Calculator.multiply(-2, 4) == -8
+        assert Calculator.multiply(0, 100) == 0
+
+    def test_divide(self):
+        """Test division."""
+        assert Calculator.divide(10, 2) == 5.0
+        assert Calculator.divide(7, 2) == 3.5
+
+    def test_divide_by_zero(self):
+        """Test that division by zero raises ValueError."""
+        with pytest.raises(ValueError, match="Cannot divide by zero"):
+            Calculator.divide(10, 0)
+
+    def test_power(self):
+        """Test power operation."""
+        assert Calculator.power(2, 3) == 8
+        assert Calculator.power(5, 2) == 25
+        assert Calculator.power(10, 0) == 1
+
+    def test_add_floats(self):
+        """Test addition with floating point numbers."""
+        result = Calculator.add(0.1, 0.2)
+        assert pytest.approx(result, 0.001) == 0.3
+
+    def test_multiply_by_zero(self):
+        """Test multiplication by zero."""
+        assert Calculator.multiply(100, 0) == 0
+        assert Calculator.multiply(0, 0) == 0
diff --git a/tests/test_string_utils.py b/tests/test_string_utils.py
new file mode 100644
index 0000000..d99a0a7
--- /dev/null
+++ b/tests/test_string_utils.py
@@ -0,0 +1,72 @@
+"""
+Tests for string utility functions.
+"""
+import pytest
+from string_utils import (
+    reverse_string,
+    is_palindrome,
+    count_vowels,
+    title_case,
+    truncate,
+)
+
+
+class TestStringUtils:
+    """Test suite for string utility functions."""
+
+    def test_reverse_string(self):
+        """Test string reversal."""
+        assert reverse_string("hello") == "olleh"
+        assert reverse_string("Python") == "nohtyP"
+        assert reverse_string("") == ""
+        assert reverse_string("a") == "a"
+
+    def test_is_palindrome_simple(self):
+        """Test palindrome detection with simple strings."""
+        assert is_palindrome("racecar") is True
+        assert is_palindrome("hello") is False
+        assert is_palindrome("A") is True
+
+    def test_is_palindrome_with_spaces(self):
+        """Test palindrome detection ignoring spaces and case."""
+        assert is_palindrome("A man a plan a canal Panama") is True
+        assert is_palindrome("race a car") is False
+
+    def test_is_palindrome_empty(self):
+        """Test palindrome with empty string."""
+        assert is_palindrome("") is True
+
+    def test_count_vowels(self):
+        """Test vowel counting."""
+        assert count_vowels("hello") == 2
+        assert count_vowels("AEIOU") == 5
+        assert count_vowels("xyz") == 0
+        assert count_vowels("") == 0
+        assert count_vowels("Python Programming") == 4
+
+    def test_title_case(self):
+        """Test title case conversion."""
+        assert title_case("hello world") == "Hello World"
+        assert title_case("python programming") == "Python Programming"
+        assert title_case("ALREADY UPPER") == "Already Upper"
+        assert title_case("") == ""
+
+    def test_truncate_short_string(self):
+        """Test truncation with string shorter than max length."""
+        assert truncate("hello", 10) == "hello"
+        assert truncate("test", 4) == "test"
+
+    def test_truncate_long_string(self):
+        """Test truncation with string longer than max length."""
+        assert truncate("hello world", 8) == "hello..."
+        assert truncate("this is a long string", 10) == "this is..."
+
+    def test_truncate_custom_suffix(self):
+        """Test truncation with custom suffix."""
+        assert truncate("hello world", 8, suffix=">>") == "hello >>
+        assert truncate("testing", 5, suffix="!") == "test!"
+
+    def test_truncate_edge_cases(self):
+        """Test truncation edge cases."""
+        assert truncate("", 5) == ""
+        assert truncate("hi", 2) == "hi"