diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
index 3ba43912..2a8b3d97 100644
--- a/.github/workflows/python-tests.yml
+++ b/.github/workflows/python-tests.yml
@@ -45,10 +45,10 @@ jobs:
         # python_tests requires optuna>=3.0.0 since it imports FloatDistribution
         run: |
           python -m pip install --progress-bar off --upgrade pip setuptools
-          pip install boto3 moto[s3]
+          pip install boto3 moto[s3] pytest
           pip install --progress-bar off "optuna>=3.0.0"
           pip install --progress-bar off .
-      - run: python -m unittest
+      - run: pytest python_tests
   test-with-optuna-master:
     runs-on: ubuntu-latest
     steps:
@@ -61,7 +61,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --progress-bar off --upgrade pip setuptools
-          pip install boto3 moto[s3]
+          pip install boto3 moto[s3] pytest
           pip install --progress-bar off .
           python -m pip install --progress-bar off --upgrade git+https://github.com/optuna/optuna.git
-      - run: python -m unittest
+      - run: pytest python_tests
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 241c80d2..034b31cd 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -76,7 +76,7 @@ Note that `OPTUNA_DASHBOARD_DEBUG=1` makes the server will automatically restart
 #### Running Python unit tests
 
 ```
-$ python -m unittest
+$ pytest python_tests/
 ```
 
 #### Running visual regression tests using pyppeteer
diff --git a/pyproject.toml b/pyproject.toml
index 406e0f49..be4a18e0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -64,13 +64,14 @@ exclude = '''
   | build
   | dist
   | venv
+  | node_modules
 )/
 '''
 
 [tool.isort]
 profile = 'black'
-src_paths = ['optuna', 'tests', 'docs', 'benchmarks']
-skip_glob = ['docs/source/conf.py', '**/alembic/versions/*.py', 'tutorial/**/*.py']
+src_paths = ['optuna', 'python_tests', 'docs']
+skip_glob = ['docs/conf.py']
 line_length = 99
 lines_after_imports = 2
 force_single_line = 'True'
@@ -80,3 +81,9 @@ order_by_type = 'False'
 [tool.mypy]
 ignore_missing_imports = true
 disallow_untyped_defs = true
+
+[tool.pytest.ini_options]
+addopts = "--color=yes"
+markers = [
+  "slow: marks tests as slow",
+]
diff --git a/requirements.txt b/requirements.txt
index 25c37877..42be1ff1 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -12,6 +12,7 @@ mypy-boto3-s3
 mypy
 
 # unit test
+pytest
 boto3
 moto[s3]