How to Create Entities with @Getter to Test a Method

My application has several entities that are annotated with @Getter and are using the @Builder. I need to create a list of Customers with specific data to test a method. I am unable create a list of OrderDetails and assign it to an Order because this property only has a getter method. I also tried mocking the objects but again I get the error unable set the property. The only way I have been able to test the method is by using an H2 database with test data. Is there another way to test my method without using an H2 database? Thanks.

@Getter
@Entity
public class Customer

private Long customerId;
private String firstName;
private String lastName;

 @OneToMany(
  mappedBy = "order",
  cascade = CascadeType.ALL,
  fetch = FetchType.EAGER)
  private List<Order> orders = new ArrayList<>();

@Builder(toBuilder = true)
  public Customer(Long customerID,
      String firstName,
      String lastName,

@Getter
@Entity
public class Order

private Long orderId;
private Long orderLocationId;
private OrderStatus orderStatus;

@ManyToOne
private Customer customer;

@OneToMany(mappedBy = "orderLine", cascade = CascadeType.ALL
private List<OrderDetails> orderDetails;

@Builder(toBuilder = true)
  public Order(OrderStatus orderStatus,
      Long orderLocationId,
      Customer customer,

@Getter
@Entity
public class OrderDetails

private Long orderDetailId;
private Long quantity;
private Instant orderTimestamp = Instant.now();

@ManyToOne
private Order order;

@Builder(toBuilder = true)
  public OrderDetails(
      Integer quantity,
      Order order) {