diff --git a/.github/workflows/python.yml b/.github/workflows/python.yml
index 43f8df7..a0b784f 100644
--- a/.github/workflows/python.yml
+++ b/.github/workflows/python.yml
@@ -77,7 +77,7 @@ jobs:
       - uses: ./.github/actions/setup-python
       - name: pytest
         working-directory: ./python
-        run: bash run_unittests.sh
+        run: pytest
   # mypy:
   #   timeout-minutes: 10
   #   runs-on: ubuntu-latest
diff --git a/python/calculator_cli_app/src/application.py b/python/calculator_cli_app/src/application.py
index 0bbb2e0..5ed3956 100644
--- a/python/calculator_cli_app/src/application.py
+++ b/python/calculator_cli_app/src/application.py
@@ -1,11 +1,6 @@
-from args_validation import __validate__
-from calculation_query import CalculationQuery
 from data_type_conversion import __to_int_with_rescue__
-import sys
-sys.path.append('./calculator_cli_app/src')
-sys.path.append('./calculator_cli_app/src/lib')
-sys.path.append('./calculator_cli_app/src/queries')
-sys.path.append('./calculator_cli_app/src/validations')
+from calculation_query import CalculationQuery
+from args_validation import __validate__
 
 
 class Application:
diff --git a/python/calculator_cli_app/test/queries/test_calculation_query.py b/python/calculator_cli_app/test/queries/test_calculation_query.py
index 5ba1748..e94aa29 100644
--- a/python/calculator_cli_app/test/queries/test_calculation_query.py
+++ b/python/calculator_cli_app/test/queries/test_calculation_query.py
@@ -1,11 +1,21 @@
+from calculation_query import CalculationQuery
 import unittest
 import sys
 from io import StringIO
 import glob
 import os
 import shutil
-sys.path.append('./src/queries')
-from calculation_query import CalculationQuery
+
+# Add src paths relative to this test file's location
+test_dir = os.path.dirname(os.path.abspath(__file__))
+module_root = os.path.dirname(os.path.dirname(test_dir))
+src_paths = [
+    os.path.join(module_root, 'src', 'queries'),
+    os.path.join(module_root, 'src')
+]
+for src_path in src_paths:
+    if src_path not in sys.path:
+        sys.path.insert(0, src_path)
 
 
 class TestCalculationQuery(unittest.TestCase):
diff --git a/python/calculator_cli_app/test/test_application.py b/python/calculator_cli_app/test/test_application.py
index 1ed1b09..eaf6354 100644
--- a/python/calculator_cli_app/test/test_application.py
+++ b/python/calculator_cli_app/test/test_application.py
@@ -1,14 +1,33 @@
+from application import Application
 import unittest
 import sys
 from io import StringIO
 import glob
 import os
 import shutil
-sys.path.append('./src')
-sys.path.append('./src/lib')
-sys.path.append('./src/queries')
-sys.path.append('./src/validations')
-from application import Application
+
+# Add src paths relative to this test file's location
+test_dir = os.path.dirname(os.path.abspath(__file__))
+module_root = os.path.dirname(test_dir)
+src_paths = [
+    os.path.join(module_root, 'src'),
+    os.path.join(module_root, 'src', 'lib'),
+    os.path.join(module_root, 'src', 'queries'),
+    os.path.join(module_root, 'src', 'validations')
+]
+
+# Remove cached modules to ensure fresh import
+for module in list(sys.modules.keys()):
+    if module in [
+        'application',
+        'data_type_conversion',
+        'calculation_query',
+            'args_validation']:
+        del sys.modules[module]
+
+for src_path in src_paths:
+    if src_path not in sys.path:
+        sys.path.insert(0, src_path)
 
 
 class TestApplication(unittest.TestCase):
diff --git a/python/fibonacci_sequence/src/fibonacci.py b/python/fibonacci_sequence/src/fibonacci.py
index b8dd637..b30ee81 100644
--- a/python/fibonacci_sequence/src/fibonacci.py
+++ b/python/fibonacci_sequence/src/fibonacci.py
@@ -1,8 +1,11 @@
+__all__ = ['fibonacci']
+
+
 def fibonacci(init_num, iter):
     current_num = init_num
     next_num = current_num + 1
     result = list()
-    for num in range(init_num, iter + init_num):
+    for _ in range(init_num, iter + init_num):
         result.append(current_num)
         current_num, next_num = next_num, current_num + next_num
     return result
diff --git a/python/fibonacci_sequence/test/test_fibonacci.py b/python/fibonacci_sequence/test/test_fibonacci.py
index 9284476..031a919 100644
--- a/python/fibonacci_sequence/test/test_fibonacci.py
+++ b/python/fibonacci_sequence/test/test_fibonacci.py
@@ -1,10 +1,16 @@
+from fibonacci import *
 import unittest
 import sys
 import glob
 import os
 import shutil
-sys.path.append('./src')
-from fibonacci import *
+
+# Add src path relative to this test file's location
+test_dir = os.path.dirname(os.path.abspath(__file__))
+module_root = os.path.dirname(test_dir)
+src_path = os.path.join(module_root, 'src')
+if src_path not in sys.path:
+    sys.path.insert(0, src_path)
 
 
 class TestFibonacci(unittest.TestCase):
diff --git a/python/fizzbuzz/src/fizzbuzz.py b/python/fizzbuzz/src/fizzbuzz.py
index 047c962..78b870d 100644
--- a/python/fizzbuzz/src/fizzbuzz.py
+++ b/python/fizzbuzz/src/fizzbuzz.py
@@ -1,3 +1,6 @@
+__all__ = ['fizzbuzz_in_if', 'fizzbuzz_in_ternary']
+
+
 def fizzbuzz_in_if(num):
     if num % 3 == 0 and num % 5 == 0:
         result = 'FizzBuzz'
diff --git a/python/fizzbuzz/test/test_fizzbuzz.py b/python/fizzbuzz/test/test_fizzbuzz.py
index 03b0c32..2da9218 100644
--- a/python/fizzbuzz/test/test_fizzbuzz.py
+++ b/python/fizzbuzz/test/test_fizzbuzz.py
@@ -1,10 +1,16 @@
+from fizzbuzz import *
 import unittest
 import sys
 import glob
 import os
 import shutil
-sys.path.append('./src')
-from fizzbuzz import *
+
+# Add src path relative to this test file's location
+test_dir = os.path.dirname(os.path.abspath(__file__))
+module_root = os.path.dirname(test_dir)
+src_path = os.path.join(module_root, 'src')
+if src_path not in sys.path:
+    sys.path.insert(0, src_path)
 
 
 class TestFizzBuzz(unittest.TestCase):
diff --git a/python/letter_inspection/test/test_application.py b/python/letter_inspection/test/test_application.py
index f361c8a..f49b214 100644
--- a/python/letter_inspection/test/test_application.py
+++ b/python/letter_inspection/test/test_application.py
@@ -1,9 +1,7 @@
 import unittest
-import sys
 import glob
 import os
 import shutil
-sys.path.append('./src')
 from application import Application
 
 
@@ -16,9 +14,11 @@ def setUp(self):
         self.pattern_1 = Application(str_1=str_1, str_2=str_2)
         self.pattern_2 = Application(str_1=str_1, str_2=str_3)
         self.pattern_3 = Application(str_1=str_1, str_2=str_4)
+        test_dir = os.path.dirname(os.path.abspath(__file__))
+        module_root = os.path.dirname(test_dir)
         self.pycaches = glob.glob(
             os.path.join(
-                '.',
+                module_root,
                 '**',
                 '__pycache__'),
             recursive=True)
diff --git a/python/letter_inspection/test/test_letter_inspection_application.py b/python/letter_inspection/test/test_letter_inspection_application.py
new file mode 100644
index 0000000..84fc186
--- /dev/null
+++ b/python/letter_inspection/test/test_letter_inspection_application.py
@@ -0,0 +1,64 @@
+from application import Application
+import unittest
+import sys
+import glob
+import os
+import shutil
+
+# Add src path relative to this test file's location
+test_dir = os.path.dirname(os.path.abspath(__file__))
+module_root = os.path.dirname(test_dir)
+src_path = os.path.join(module_root, 'src')
+
+# Remove cached modules to ensure fresh import
+for mod in list(sys.modules.keys()):
+    if mod == 'application':
+        del sys.modules[mod]
+
+if src_path not in sys.path:
+    sys.path.insert(0, src_path)
+
+
+class TestApplication(unittest.TestCase):
+    def setUp(self):
+        str_1 = 'hogefoobar'
+        str_2 = 'abefghooor'
+        str_3 = 'hoge'
+        str_4 = 'piyopoopee'
+        self.pattern_1 = Application(str_1=str_1, str_2=str_2)
+        self.pattern_2 = Application(str_1=str_1, str_2=str_3)
+        self.pattern_3 = Application(str_1=str_1, str_2=str_4)
+        self.pycaches = glob.glob(
+            os.path.join(
+                '.',
+                '**',
+                '__pycache__'),
+            recursive=True)
+
+    def tearDown(self):
+        for pycache in self.pycaches:
+            if os.path.exists(pycache):
+                shutil.rmtree(pycache)
+
+
+class TestRegularCase(TestApplication):
+    def test_exactly_equal_size_and_included_1(self):
+        self.assertTrue(self.pattern_1.exactly_equal_size_and_included())
+
+
+class TestIrregularCase(TestApplication):
+    pass
+
+
+class TestCase1(TestIrregularCase):
+    def test_exactly_equal_size_and_included_2(self):
+        self.assertFalse(self.pattern_2.exactly_equal_size_and_included())
+
+
+class TestCase1(TestIrregularCase):
+    def test_exactly_equal_size_and_included_3(self):
+        self.assertFalse(self.pattern_3.exactly_equal_size_and_included())
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/python/nabeatsu/src/nabeatsu.py b/python/nabeatsu/src/nabeatsu.py
index 2dee77a..4676d4a 100644
--- a/python/nabeatsu/src/nabeatsu.py
+++ b/python/nabeatsu/src/nabeatsu.py
@@ -1,3 +1,6 @@
+__all__ = ['go_crazy_in_if', 'go_crazy_in_ternary']
+
+
 def go_crazy_in_if(num):
     if num % 3 == 0 or '3' in str(num):
         # Express the status of 'crazy' with '!'
diff --git a/python/nabeatsu/test/test_nabeatsu.py b/python/nabeatsu/test/test_nabeatsu.py
index 00de333..1f5ea16 100644
--- a/python/nabeatsu/test/test_nabeatsu.py
+++ b/python/nabeatsu/test/test_nabeatsu.py
@@ -1,10 +1,16 @@
+from nabeatsu import *
 import unittest
 import sys
 import glob
 import os
 import shutil
-sys.path.append('./src')
-from nabeatsu import *
+
+# Add src path relative to this test file's location
+test_dir = os.path.dirname(os.path.abspath(__file__))
+module_root = os.path.dirname(test_dir)
+src_path = os.path.join(module_root, 'src')
+if src_path not in sys.path:
+    sys.path.insert(0, src_path)
 
 
 class TestNabeatsu(unittest.TestCase):
diff --git a/python/pyproject.toml b/python/pyproject.toml
new file mode 100644
index 0000000..b3ad617
--- /dev/null
+++ b/python/pyproject.toml
@@ -0,0 +1,11 @@
+[tool.mypy]
+python_version = "3.14"
+warn_return_any = true
+warn_unused_configs = true
+disallow_untyped_defs = true
+
+[tool.pytest.ini_options]
+# Configure pytest to properly handle module discovery
+python_files = ["test_*.py"]
+python_classes = ["Test*"]
+python_functions = ["test_*"]
diff --git a/python/run_unittests.sh b/python/run_unittests.sh
deleted file mode 100644
index 74f7a91..0000000
--- a/python/run_unittests.sh
+++ /dev/null
@@ -1,8 +0,0 @@
-#!/bin/sh
-
-for directory in $(ls -d */)
-do
-  cd $directory
-  python -m unittest discover ./test
-  cd ../
-done