Fix lint errors

tests/__init__.py

@@ -1,5 +1,7 @@
 #!/usr/bin/env python3
 
+"""PyTest unit tests."""
+
 import pytest
 
 from app.app import app
@@ -7,5 +9,6 @@ from app.app import app
 
 @pytest.fixture
 def client():
+    """Set up Flask client for use in tests."""
     client = app.test_client()
     yield client