feat: testing tutorial

src/tutorial/testing/shop/pricing.py

@@ -0,0 +1,2 @@
+def discount_price(price: float, percent: float) -> float:
+    return price - price * percent / 100

tests/test_tutorial/shop/test_pricing.py

@@ -0,0 +1,6 @@
+from src.tutorial.testing.shop.pricing import discount_price
+
+
+def test_discount_price_reduces_price():
+    result = discount_price(100.0, 20.0)
+    assert result == 80