Implementing Testing Strategies

@Test
void placesOrderWithCorrectTotal() {
    var cart = Cart.of(Item.of("sku1", 2, money(10_00)));
    var order = service.place(cart);
    assertThat(order.total()).isEqualTo(money(20_00));
    assertThat(order.status()).isEqualTo(PLACED);
}

@ExtendWith(MockitoExtension.class)
class OrderServiceTest {
    @Mock InventoryClient inventory;
    @InjectMocks OrderService service;

    @Test void reservesInventory() {
        when(inventory.reserve("sku1", 2)).thenReturn(reservation("r1"));
        service.place(Cart.of(Item.of("sku1", 2, money(100))));
        verify(inventory).reserve("sku1", 2);
    }
}

public class OrderTestBuilder {
    private UUID id = UUID.randomUUID();
    private List<Item> items = List.of(Item.of("sku1", 1, money(10_00)));
    public static OrderTestBuilder anOrder() { return new OrderTestBuilder(); }
    public OrderTestBuilder withItems(Item... it) { this.items = List.of(it); return this; }
    public Order build() { return new Order(id, items); }
}
// Usage: anOrder().withItems(item("sku2", 5)).build();